Chap 2 : Acid Bases and Salts www.cbse.

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CHAPTER 2
Acid Bases and Salts

1. ONE MARK QUESTIONS H+(aq) ions in a solution have on pH of solution?

Ans : [CBSE 2013,2009]
Increase in H+ concentration will lead to decrease in
1. Write chemical equation for the reaction of zinc metal pH,
on sodium hydroxide.
Ans : [CBSE 2016] 10. Name a gas evolved when dilute HCl reacts with
Heat sodium hydrogen carbonate. How is it recognised?
Zn(s) + 2NaOH(aq) Na2ZnO2(aq) + H2(g)
Ans : [CBSE 2013]
2. Three acidic solutions A, B and C have pH = 0, 3 and Carbon dioxide, it turns lime water milky. In this way,
5 respectively. CO2 gas is recognised.
a. Which solution has the highest concentration of
H+ ions? 11. What are olfactory indicators?
b. Which solution has the lowest concentration of Ans : [CBSE 2013]
H+ ions?
Those indicators whose smell changes in acidic and
Ans : [CBSE 2015] basic solutions.
a. The solution with pH = 0 has highest concentration
of H+ ions. 12. Why does 1 M HCl solution have a high concentration
b. The solution with pH = 5 has lowest concentration of H+ ions than 1 M CH3COOH solution?
of H+ ions. Ans : [CBSE 2013,2009]
It is because 1M HCl is a strong acid and it is completely
3. What is meant by p and H in pH?
ionised in aqueous solution whereas CH3COOH is a
Ans : [CBSE 2014] weak acid, so it is only partially ionised.
p stands for ‘potenz’ in German meaning power, H
stands of hydrogen.

4. Define alkalies and give an example.

Ans : [CBSE 2014]
Water soluble bases are called alkalies e.g., NaOH.

5. Mention the range of pH for identification of a base.

Ans : [CBSE 2014]
7.1 to 14 is the pH range for bases.

6. How chloride of lime differs from calcium chloride?

Ans : [CBSE 2014]
CaOCl2 is the chloride of lime whereas CaCl2 calcium
chloride. 13. Write the chemical equation representing the action of
atmospheric CO2 gas on bleaching powder when left
7. What is meant by water of crystallisation in a exposed in open.
substance?
Ans : [CBSE 2013]
Ans : [CBSE 2014]
CaOCl2 + CO2 $ CaCO3 + Cl2
The water molecules associated with a crystalline
solid are called water of crystallisation. 14. How will you test for the gas which is liberated when
hydrochloric acid reacts with an active metal?
8. Write the chemical name and chemical formula of
washing soda. Ans : [CBSE 2012,2009]
Ans : [CBSE 2014] Bring a burning matchstick near the gas. If it is burnt
with ‘pop’ sound, the gas is H2.
Na2CO3.10H2O, sodium carbonate deca-hydrate is
washing soda. 15. How is the pH of solution of an acid influenced when

9. What effect does an increase in concentration of

 it is diluted? family.
Ans : [CBSE 2012] Ans : [CBSE 2011]
pH of the solution increases when it is diluted. NaCl, Na2CO3 are two salts belonging to sodium
family.
16. At what pH rain water is said to be acidic ?
Ans : [CBSE 2012] 26. Which among distilled water, tap water and sea water
is the best conductor of electricity?
When pH < 5.5, the rain water becomes acidic.
Ans : [CBSE 2010, 2011]
17. Which gas is evolved when dilute hydrochloric acid Sea water is a better conductor due to the presence
reacts with zinc metal? Write the molecular formula of ions.
of this gas.
Ans : [CBSE 2012] 27. Name the acids present in (i) nettle sting, (ti) curd.

Dihydrogen gas, H2. Ans : [CBSE 2010]

(i) HCOOH, Formic acid,
18. Dry HCl gas does not change the colour of dry blue (ii) Lactic acid, CH3-CH(OH)-COOH
litmus. Give reason to justify it.
Ans : [CBSE 2012] 28. Name a salt which does not contain water of
crystallisation.
Dry HCl (g) does not form ions, therefore it does not
affect dry blue litmus. Ans : [CBSE 2010]
NaHCO3 is a salt that does not contain water of
19. Why is HCl a stronger acid than acetic acid? crystallisation.
Ans : [CBSE 2012]
29. Write the name and chemical formula of the product
HCl is completely ionised in aqueous solution whereas
formed by heating gypsum at 373 K.
acetic acid is only partially ionised in aqueous solution.
Ans : [CBSE 2010]
20. Name the chemicals used in acid fire extinguisher and Plaster of Paris, CaSO . H2O1
4 2
the gas evolved from it when it is used?
Ans : [CBSE 2012, 2011] 30. The pH of a sample of vegetable soup was found to be
6.5. How is this soup likely to taste?
NaHCO3 (Sodium hydrogen carbonate) and H2SO4
(Sulphuric acid). The gas evolved is carbon dioxide. Ans : [CBSE 2010]
It will be sour in taste.
21. Which is a stronger acid, with pH = 5 or with pH=2?
Ans : [CBSE 2011] 31. Which bases are called alkalies? Give one example of
alkali.
The acid with pH = 2 is a stronger acid.
Ans : [CBSE 2010,2009]
22. A compound which is prepared from gypsum has Those bases which are soluble in water are called
the property of hardening when mixed with a proper alkalies e.g., NaOH, KOH.
quantity of water. Identify the compound and write
its chemical formula. 32. Write the name and chemical formula of the product
Ans : [CBSE 2011] formed by action of chlorine on slaked lime.
CaSO4. 12 H2O (Plaster of Paris), Calcium sulphate Ans : [CBSE 2010]
hemihydrate. CaOCl2, Bleaching powder, Calcium oxy-chloride.

23. What is meant by term pH of solution? The pH of 33. Write a balanced chemical equation for the reaction
rain water collected from two cities A’ and ‘B’ were between sodium carbonate and hydrochloric acid
found to be 6.0 and 5.0 respectively. The water of indicating the physical state of reactants and the
which city will be more acidic? products.
Ans : [CBSE 2011] Ans : [CBSE 2010]
pH of solution is defined as negative logarithm of H+ Na 2 CO 3 (s) + 2HCl (dill) $ 2NaCl (aq) + CO 2 (g) + H 2 O (l)
ion concentration. It determines the strength of acid
and base. Rainwater with pH = 5 is more acidic. 34. Name the acid and base that have constituted the salt
ammonium nitrate.
24. A few drops of sulphuric acid are added to water Ans : [CBSE 2010]
before electrolysis, why?
Acid: HNO3,
Ans : [CBSE 2011] Base: NH4OH (i.e., Nitric acid, Ammonium hydroxide).
Water is not a good conductor of electricity. Few
drops of sulphuric acid makes it better conductor of 35. Suggest one way to reduce alkaline nature of the soil.
electricity. Ans : [CBSE 2010]
Add ammonium nitrate (Acidic salt) to neutralise
25. Write the names of two salts belonging to sodium
alkaline nature of soil.
36. Oxides of metals are basic while those of non-metals 46. How does the pH change when solution of a base is
are acidic. Explain. diluted?
Ans : [CBSE 2010] Ans : [CBSE 2008]
Metal oxides dissolve in water to form base basic in When solution of a base is diluted, its pH decreases.
nature. On the other hand non-metals dissolve in
water to form acids, acidic in nature. 47. Arrange the following in an increasing order of their
pH values: NaOH solution, Blood, Lemon juice.
37. What is the difference between slaked lime and lime Ans : [CBSE 2008]
water?
Lemon juice < Blood < NaOH solution.
Ans : [CBSE 2010]
The solid Ca(OH)2 is slaked lime whereas clear 48. At what pH in the mouth is tooth decay faster and
solution of Ca(OH)2 in water is lime water. why?
Ans : [CBSE 2008]
38. Write a balanced chemical equation for the
At pH lower than 5.5, tooth decay becomes faster
neutralisation reaction, mentioning the physical state
because calcium phosphate (enamel) reacts with acid
of reactants and products.
and gets corroded.
Ans : [CBSE 2010]
NaOH(aq) + HCl(aq) $ NaCl(aq) + H2O(l)
TWO MARKS QUESTIONS
39. During summer season, a milkman usually adds a very
small amount of baking soda to fresh milk. Give one
reason. 49. A white chemical compound becomes hard on mixing
proper quantity of water. It is also used to maintain
Ans : [CBSE Sample Paper 2009]
joints in fixed position. Name the chemical compound
Baking soda is basic in nature, it will not allow milk and write its chemical formula. Write the chemical
to turn sour due to the formation of lactic acid. equation to show what happens when water is added
to this compound in proper quantity.
40. Curd is not kept in copper and brass utensils, why?
Ans : [CBSE Sample Paper 2018, CBSE 2016]
Ans : [CBSE 2009C]
CaSO4. 12 H2O is the formula of the compound. The
Curd contains lactic acid which can make poisonous name of compound is ‘Plaster of Paris’ (Calcium
compounds with brass and copper vessels. sulphate hemihydrate).
41. Fresh milk has pH = 6. When it changes to curd will
CaSO 4 $ 12 H 2 O + 32 H 2 O $ CaSO 4 $ 2H 2 O
(Plaster of Paris) (Gypsum)
its pH value increase or decrease? 50. Two solutions ‘A’ and ‘B’ have pH value 3.0 and 10.5
Ans : [CBSE 2009] respectively. Which of these will turn
pH value will decrease when milk changes to curd. a. Blue litmus solution to red,
b. Phenolphthalein from colourless to pink? Justify
42. What would be the colour of litmus in a solution of your answer in each case.
sodium carbonate? Ans : [CBSE 2016]
Ans : [CBSE 2009] a. ‘A’ with pH = 3, will turn blue litmus red because
The red litmus will turn blue in Na2CO3 solution. it is acidic in nature.
b. “B’ with pH = 10.5, will turn phenolphthalein
43. What is the colour of litmus in a solution of ammonium colourless to pink because ‘B’ is basic in nature.
hydroxide?
Ans : [CBSE 2009] 51. The pH of soil ‘A’ is 7.5, while that of soil “B is 4.5.
Which of the two soils A or B should be treated with
Red litmus will turn blue green colour in a solution of
powdered chalk to adjust the pH and why?
ammonium hydroxide.
Ans : [CBSE 2016]
44. On adding dilute hydrochloric acid to copper oxide Soil ‘B’ is acidic, therefore it needs to be treated with
powder, the solution formed is blue green. Predict the powdered chalk to adjust its pH because chalk is basic,
new compound formed which imparts a blue green which will make soil neutral.
colour to the solution.
Ans : [CBSE 2008] 52. Write the chemical equation to describe how baking
soda is produced on a large scale. Also write the
Copper chloride imparts blue green colour to the
chemical name of the products formed in the reaction.
solution.
Ans : [CBSE 2016]
45. How does flow of acid rain water into river makes the NH 3 + H 2 O + CO 2 + NaCl $ NaHCO 3 + NH 4 Cl
survival of aquatic life in the river difficult? (Sodium hydrogen (Ammonium
carbonate) chloride)
Ans : [CBSE 2008]
Acidic water makes aquatic species uncomfortable. 53. What is chlor-alkali process? Write a balanced
Aquatic species are more comfortable in the pH 7 to chemical equation for the reaction involved in this
7.8.
 process, to justify your answer. Ans : [CBSE 2016]
Ans : [CBSE 2016] a. Green precipitate of Fe(OH)2 will be formed:
When brine solution is electrolysed we get alkali FeSO 4 (aq) + 2NaOH (aq) $ Fe (OH) 2 . Na 2 SO 4 (aq)
(Green ppt)
(NaOH) and chlorine (Cl2) gas, this process is called
chlor-alkali process. b. White precipitate of Al(OH)3 will be formed:
2NaCl (aq) + 2H 2 O (l) $ 2NaOH (aq) + H 2 (g) + Cl 2 (g) AlCl (aq) + 3NaOH $ Al (OH) 3 (s) + 3NaCl (aq)
(White ppt)

54. What is meant by the term water of crystallisation? 60. 15 mL of water and 10 mL of sulphuric acid are to be
How would you show that copper sulphate crystals mixed in a beaker
contains water of crystallisation? a. State the method that should be followed with
Ans : [CBSE 2016] reason.
b. What is this process called?
The molecules of water associated with a crystalline
Ans : [CBSE 2015]
substance are called water of crystallisation.
When hydrated copper sulphate is heated its colour a. Acid should be added to the water slowly with
changes from blue to dirty white and water droplets constant cooling because the reaction is highly
are formed. exothermic.
CuSO4.5H2O
Heat
CuSO4 + 5H2O b. This process is called dilution.
If we add little water to anhydrous CuSO4, we get blue
colour again. It is the presence of molecules of water of
crystallisation which was lost on heating.
CuSO4 + 5H2O $ CuSO4.5H2O
(Anhydrous)

55. Mention the pH of aqueous solution of the following

salts as 7, more than 7, less than 7.
KCl, Na2CO3, NH4C1, NaNO3 (Sodium nitrate)
Ans : [CBSE 2016]
KCl and NaNO3 has pH = 7
Na2CO3 has pH > 7
NH4Cl has pH < 7

56. You have two solutions A and B. The pH of solution

‘A’ is 6 and the pH of solution ‘B’ is 8. Which solution 61. Name the acid present in the following:
has more hydrogen ion concentration? Which one of a. Tomato,
this is acidic and which one is basic? b. Vinegar,
Ans : [CBSE 2016] c. Tamarind
‘A’ has more H+ ion concentration. Ans : [CBSE 2015]
‘A’ is acidic while ‘B’ is basic. a. Tomato contains oxalic acid.
b. Vinegar contains acetic acid.
57. Give suitable reasons to justify the following statement:
c. Tamarind contains tartaric acid.
An aqueous solution of sodium chloride is neutral but
an aqueous solution of sodium metal is basic. 62. Explain how antacid works.
Ans : [CBSE 2016] Ans : [CBSE 2015]
Sodium chloride is made up of a strong base, NaOH Antacids are weakly basic in nature. They neutralise
and a strong acid, HCl. Therefore, its aqueous solution excess of HCl present in our stomach and gives us
is neutral in nature. relief from hyper-acidity.
Sodium metal reacts with water to form NaOH(Base)
and H2 gas: 63. Equal lengths of magnesium ribbon are taken in test
2Na (s) + 2H 2 O (l) $ 2NaOH (aq) + H 2 (g) tube ‘A’ and ‘B’. Hydrochloric acid (HCl) is added to
test tube A’ while acetic acid (CH3COOH) is added
58. What is the action of litmus on to test tube ‘B’. In which test tube, will fizzing occur
a. dry ammonia gas more vigorously and why?
b. solution of ammonia gas in water? Ans : [CBSE 2015]
Ans : [CBSE 2016]
The fizzing will occur more vigorously in test tube ‘A’
a. There is no effect of dry litmus on dry ammonia because HCl is a strong acid and reacts faster than
gas. acetic acid which is a weak acid.
b. Solution of ammonia will turn red litmus blue.
64. State what does pH of solution signify? Three solutions
59. State the observations you would make on adding A, B and C have pH values of 6, 2 and 10 respectively.
sodium hydroxide to an aqueous solution of Which one of these solutions is highly acidic? Which
a. ferrous sulphate, solution will turn red litmus blue?
b. aluminium chloride. Ans : [CBSE 2015]
 pH of solution signifies the nature of the solution i.e., place when it is heated.
it is weakly acidic, strongly 1 acidic, neutral, weakly Ans : [CBSE 2013, 2008(C)]
basic, strongly basic.
‘X’ is NaHCO3, sodium hydrogen carbonate. It is used
‘B’ with pH = 2 is strongly acidic.
in cooking and for curing acidity in stomach.
‘C’ with pH = 10 will turn red litmus blue. Heat
2NaHCO3 Na2CO3 + CO2 +H2O
65. Define an acid and a base. Name one weak acid and
one strong acid. 72. Crystals of a substance changes their colour on heating
in a closed vessel but regained it after sometime, when
Ans : [CBSE 2015]
they were allowed to cool down.
Acid is a substance which gives H+ ions in an aqueous a. Name one such substance.
solution. b. Explain the phenomenon involved.
Base is substance which gives OH- ions in the aqueous Ans : [CBSE 2012]
solution.
CH3COOH is a weak acid, H2SO4 is a strong acid. a. CuSO4.5H2O (Hydrated copper sulphate)
Heat
b. CuSO4.5H2O CuSO4 + 5H2O
Blue (Dirty white)
66. What is universal indicator? State the purpose for
which this indicator is used. The colour changes due to the loss of molecules
of water of crystallisation. Colour is regained by
Ans : [CBSE 2015]
absorbing water molecules from the atmosphere
Universal indicator is a mixture of a number of containing water vapours.
indicators. It is used to determine pH of a solution.
73. (a) Write the name given to the bases that are highly
67. Name the natural source of each of the following acid: soluble in water. Give an example.
a. Citric acid, (b) Why does bee sting causes pain and irritation?
b. Oxalic acid, Rubbing of baking soda on the sting area gives
c. Lactic acid, relief. How?
d. Tartaric acid. Ans : [CBSE 2012]
Ans : [CBSE 2014]
(a) Highly soluble bases are called alkalies e.g., KOH.
a. Citric acid—Lemon, Orange. (b) Bee sting contains HCOOH, formic acid which
b. Oxalic acid—Tomato, Guava causes irritation. Baking soda (basic) neutralises
c. Lactic acid—Curd, Sour milk HCOOH, therefore it gives relief from pain on
d. Tartaric acid—Tamarind rubbing it on sting area,
68. Explain why sodium hydroxide solution cannot be 74. The pH of the mouth of a person is lower I than 5.5.
kept in aluminium containers? Write the equation for What changes will occur in his mouth? How these
the reaction that may take place for the same. changes can be controlled? Write any two measures.
Ans : [CBSE 2014] Ans : [CBSE 2012, 2011, 2010]
It because ‘Al’ reacts with NaOH to form sodium Acid will be formed in the mouth which causes tooth
meta-aluminate and hydrogen gas: decay.
2Al + 2NaOH + 2H2O $ NaAlO2+3H2 a. Wash your mouth with water after every meal.
b. Brush your teeth after meal. Toothpastes are basic
69. A student detected the pH of four unknown solutions in nature and it will neutralise the acid formed in
A, B, C and D as follows: 11, 5, 7 and 2. Predict the mouth.
nature of these solutions.
Ans : [CBSE 2013] 75. What is a neutralisation reaction? Give one example.
pH = 11 is basic Ans : [CBSE 2011 ]
pH = 5 is acidic The reaction in which acid reacts with a base to form
pH = 7 is neutral salt and water is called neutralisation reaction e.g.,
pH = 2 is strongly acidic KOH(aq) + HNO3(aq) $ KNO3(aq) + H2O(l)
70. Give two uses of baking soda and washing soda each. 76. Write the chemical name of Plaster of paris. Write
Ans : [CBSE 2013] a chemical equation to show the reaction between
Plaster of paris and water.
Use of baking soda:
a. It is used in making of bread, biscuits, cakes. Ans : [CBSE 2011]
b. It is used as an antacid. CaSO 4 $ 12 H 2 O (Calcium sulphate hemihydrate)
Use of washing soda:
a. It is used as a cleansing agent. CaSO 4 $ 12 H 2 O + 32 H 2 O $ CaSO 4 $ 2H 2 O
b. It is used to remove hardness of water.
77. State in brief the preparation of washing soda from
71. A compound ‘X’ of sodium is commonly used for baking soda. Write balanced chemical equation of the
making crispy pakoras. It is also used for curing reaction involved.
acidity in the stomach. Identify ‘X’. Write the formula Ans : [CBSE 2011]
and its chemical name. State the reaction which takes When sodium hydrogen carbonate (Baking soda)
 is heated sodium carbonate is formed which on oxychloride
crystallisation forms washing soda: Ca(OH)2 + Cl2 $ CaOCl2 + H2O
(Dry slaked lime)
Heat
2NaHCO 3 Na 2 CO 3 + CO 2 + H 2 O It is used as a disinfectant i.e., it makes water fit for
(Baking soda)
drinking.
Na CO + 10H 2 O $ Na 2 CO 3 $ 10H 2 O
2 3
(Washing soda) 84. What are olfactory indicators? Dry HCl gas does not
78. What is colour of FeSO4.7H2O crystals? How does this change the colour of dry blue litmus. Give reason.
colour change upon heating? Give a balanced chemical Ans : [CBSE 2011]
equation for the change.
Ans : [CBSE 2011] Olfactory indicators: They give different smell in acids
and bases.
FeSO4.7H2O is pale green in colour. It becomes dirty
white on heating. Dry HCl(g) does not form ions, so there is no
FeSO4.7H2O $ FeSO4 + 7H2O effect on litmus.
If it is heated strongly Fe2O3 and SO2, SO3 gases will
be formed .
Heat
2FeSO4 Fe2O3 + SO2 + SO3

79. Classify the following salts into acidic, basic and

neutral salts: Potassium sulphate, ammonium chloride,
sodium carbonate, sodium chloride
Ans : [CBSE 2011]
Acidic: Ammonium chloride,
Basic: Sodium carbonate,
Neutral: Potassium sulphate, sodium chloride.

80. A student dropped few pieces of marble in dilute HCl

contained in a test tube. The evolved gas was passed
through lime water.
85. Answer the following:
a. What change would be observed in lime water?
a. Why is Plaster of paris written as CaSO 4 $ 12 H 2 O
b. Write a balanced chemical equation for the above
? How is it possible to have a half water molecule
change.
attached with CaSO4?
Ans : [CBSE 2011] b. Why is sodium hydrogen carbonate an essential
a. Lime water will turn milky. ingredient in antacids?
b. Ca(OH)2(aq) + CO2(g) $ CaCO3(s) + H2O(l) Ans : [CBSE 2011,2010]
81. A white powder is added while baking breads and a.It has one molecule of water associated with 2
while making cakes to make them soft and fluffy. molecules of CaSO4. Water molecules are present
What is the name of that powder? What are the as water of crystallisation.
main ingredients in it? What are the functions of each b. It is a mild base and it can neutralise hyper acidity
ingredient? without harming our body.
Ans : [CBSE 2011,2010] 86. What happens when chlorine is passed over slaked
The powder is baking powder. It consist of sodium lime at 313 K? Write chemical equation of the reaction
hydrogen carbonate and tartaric acid. involved and state two uses of the product.
NaHCO3 gives CO2 on heating which makes the Ans : [CBSE 2010]
bread cake soft and fluffy. Tartaric acid neutralises Bleaching powder, CaOCl2 is formed:
Na2CO3 which is bitter in taste. Ca(OH)2 + Cl2
3313 K
CaOCl2 + H2O
a. It is used as an oxidising agent.
82. HCl and HNO3 show acidic characteristics in aqueous
b. It is used as a disinfectant.
solution while alcohol and glucose solutions do not.
Give reasons. 87. What is meant by ‘water of crystallisation’ of
Ans : [CBSE 2011] a substance? Describe an activity to show that
HCl and HNO3 form H or H3O ions in aqueous
+ + blue copper sulphate crystals contains water of
solution whereas alcohol and glucose do not dissociate crystallisation.
into ions. Ans : [CBSE 2009]
HCl + H2O $ H3O+ + Cl- The molecules of water associated with a crystalline
HNO3 + H2O $ H3O + NO + - substance are called ‘water of crystallisation.’
3
CuSO 4 $ 5H 2 O $ CuSO 4 + 5H 2 O
83. What is bleaching powder chemically? Give a reaction When hydrated copper sulphate is heated its colour
for its preparation. State one of its use. changes from blue to dirty white and water droplets
Ans : [CBSE 2011] are formed. If we add little quantity of water to
anhydrous CuSO4, we get blue colour again. It is those
Bleaching powder is chemically CaOCl2, calcium
 presence of molecules water of crystallisation which chemical equation for its formation. List its two uses.
was lost on heating. Ans : [CBSE 2018]
Activity: To study the effect of heat on hydrated
The salt is NaHCO3, sodium hydrogen carbonate.
crystalline salts.
NH 3 (g) + CO 2 (g) + NaCl (g) + H 2 O (l) $ NaHCO 3 (s) + NH 4 Cl
i. Take 2 g of CuSO 4 $ 5H 2 O in a test tube.
Uses:
ii. Observe the initial colour of the salt.
a. It is used as an antacid.
iii. Heat the test tube at top of burner carefully as
b. It is used in soda-acid fire extinguishers.
shown in the diagram.
iv. Record your observations. No salt has pH = 14. NaHCO3 has pH = 8.4.
v. Cool the crystals and add few drops of water.
vi. Record your observations again. 92. (a) Why does aqueous solution of an acid conduct
Observations: Blue colour of CuSO 4 $ 5H 2 O is changed electricity?
to dirty white anhydrous CuSO4 and water droplets (b) How does the concentration of H3O+ ions change
were formed. On adding water, blue colour of salt was when a solution of an acid is diluted?
restored. (c) Which one has a higher pH, a concentrated or a
Conclusion: CuSO 4 $ 5H 2 O is a hydrated salt which dilute solution of hydrochloric acid?
loses water of crystallisation, which on heating (d) What would to be the gas evolved on adding
becomes dirty white and regains its colour when it dilute to hydrochloric acid to
comes in contact with water. (i) Solid sodium carbonate placed in a test tube?
Chemical reactions involved: (ii) Zinc metal in a test tube?
Heat Ans : [CBSE 2018(C)]
CuSO 4 $ 5H 2 O (S) CuSO 4 (s) + 5H 2 O (l)
(Blue) (Dirty white) a. It contains ions which carry current.
CuSO 4 (s) + 5H 2 O (l)
Heat
CuSO 4 $ 5H 2 O b. H3O+ ions will decrease when it is 7 diluted.
(Blue) c. Dilute solution has higher pH than concentrated.
88. Write the chemical formulae of washing soda and d. (i) CO2 gas will be formed:
baiting soda. Which one of these two is an ingredient Na2CO3 + 2HCl $ 2NaCl + H2O + CO2
of antacids? How does it provide relief in stomachache? (ii) Hydrogen gas will be formed:
Ans : [CBSE 2000] Zn + 2HCl $ ZnCl2 + H2
Na 2 CO 3 $ 10H 2 O is washing soda, NaHCO3 is baking 93. pH has a great importance in our daily life. Explain
soda. NaHCO3 is an ingredient of antacid. It neutralises by giving three examples.
hyper acidity in stomach and gives relief. Ans : [CBSE Sample Paper 2018]
89. What is baking powder? How does it make the cake a. pH of our stomach is 2.0 and it is needed for the
soft and spongy? digestion of proteins in our body.
Ans : [CBSE 2008] b. Blood has pH = 7.36 to 7.42 which must be
maintained for proper health.
Baking powder is made up of NaHCO3 and tartaric
c. pH of soil is determined and suitable chemicals
acid. NaHCO3, on heating gives CO2 which makes the
are added so as to make it suitable for growth of
cake soft and spongy.
crops.

94. Answer the following questions:

THREE MARKS QUESTIONS a. State the colour of phenolphthalein in soap
solution.
b. Name the by-product of chlor-alkali process which
90. 2 mL of sodium hydroxide solution is added to a few is used for the manufacture of bleaching powder.
pieces of granulated zinc metal taken in a test tube. c. Name one indicator which specifies the various
When the contents are warmed, a gas evolves which is levels of H+ ion concentration.
bubbled through a soap solution before testing. Write Ans : [CBSE 2016]
the equation for the chemical reaction involved and a. Phenolphthalein will turn pink in soap solution.
the test to detect the gas. Name the gas which will b. Chlorine is the by-product of chlor-alkali process
be evolved when the same metal reacts with dilute which is used in the manufacture of bleaching
solution of a strong acid. powder.
Ans : [CBSE 2018] c. Universal indicator specifies the various levels of
Zn (s) + 2NaOH
Worm
Na ZnO + H 2 H+ ion concentration.
2 2
(Sodium zincate)

Test: Bring a burning splinter near the gas. If it burns 95. a. Define a universal indicator. Mention its one use.
with ‘pop’ sound, the gas liberated is hydrogen. b. Solution ‘A’ gives pink colour when a drop of
Zn + H2SO4(dil) $ ZnSO4(aq) + H2 phenolphthalein indicator is added to it. Solution
Hydrogen gas will be evolved by reaction of the same ‘B’ gives a red colour when a drop of methyl
metal with dilute H2SO4, strong acid. orange is added to it. What type of solutions are
‘A’ and ‘B’ and which of these will have higher
91. The pH of a salt which is used to make tasty and pH?
crispy pakoras is 14. Identify the salt and write a c. Name one salt whose solution has pH greater than
 7 and one salt with pH less than 7.
CuSO 4 (s) + 5H 2 O (l) $ CuSO 4 $ 5H 2 O
Ans : [CBSE 2016] Blue

a. Universal indicator is mixture of indicators used b. Na2CO3.10H2O, washing soda (Sodium carbonate
to find pH of solution. It is used to measure levels decahydrate) has 10 molecules of water of
of H+ ion concentration. crystallisation. CaSO4.2H2O, gypsum, chemically
b. ‘A’ is basic in nature, ‘B’ is acidic in nature. ‘A’ calcium sulphate dihydrate has 2 molecules of
will have higher pH than ‘B’. It should be greater water of crystallisation.
than 7.
100. You are provided with magnesium ribbon and sulphur
c. Na2CO3 is the salt whose pH is more than, CuSO4
powder. Explain with the help of activity that metal
is the salt whose pH is less than 7.
oxides are basic and oxides of non-metals are acidic
96. a. Define pH scale. Draw a figure showing variation in nature.
of pH with change in concentration of H+(aq) and Ans : [CBSE 2014]
OH-(aq) ions. Bum magnesium ribbon with the help of tongs to
b. Mention the pH of acidic, basic and neutral form white ash. Dissolve the ash in hot water. Add
solutions respectively. red litmus which turns blue, showing that MgO is a
Ans : [CBSE 2016] basic oxide.
a. pH scale is a scale which is used for measuring 2Mg(s) + O2(g) $ 2MgO(s)
hydrogen ion concentration in a solution. MgO(s) + H2O(Hot) $ Mg(OH)2(aq)
Heat sulphur taken in a iron spatula and pass the gas
through water. Add blue litmus into it. It will turn red
showing SO2 is an acidic oxide.
S + O2 $ SO2
SO2 + H2O $ H2SO3 (Sulphurous acid)
b. pH < 7 is for acidic solution, pH > 7 basic solution, 101. List two differences between acids and bases on the
pH = 7 for neutral solution. basis of chemical properties.
97. a. Define olfactory indicators. Name two substances Ans : [CBSE 2013]
which can be used as olfactoiy indicators.
b. Choose strong acids from the following: Acids Bases
CH3COOH, H2SO4, H2CO3, HNO3 1. Acids turn blue litmus Bases turn red litmus
Ans : [CBSE 2015] red. blue.
a. Olfactory indicators: They give different smell in 2. Acids liberate CO2 Bases do not react
acidic and basic medium e.g., onion, clove, vanilla. with metal carbonates with metal carbonates
b. HNO3 and H2SO4 are strong acids among the given and hydrogen and hydrogen
acids. carbonates. carbonates.
98. Explain the action of dilute hydrochloric acid on the
following with suitable chemical equations: 102. A substance ‘X’ is used as antacid reacts with
a. Magnesium ribbon, hydrochloric acid to produce a gas W which is used in
b. Sodium hydroxide, fire extinguishers:
c. Crushed egg shells. a. Name the substance X and ‘Y’.
b. Write a balanced equation of the reaction between
Ans : [CBSE 20151
X and hydrochloric acid.
a. Mg(s) + 2HCl(dil) $ MgCl2(aq) + H2(g) Ans : [CBSE 2013]
b. NaOH(aq) + HCl(dil) $ NaCl(aq) + H2O(l)
c. CaCO 3 ^ s h + 2HCl ^dilh $ CaCl 2 ^gh + CO 2 ^gh + H 2 O ^ l h a. ‘X’ is NaHCO3 (Sodium hydrogen carbonate). ‘Y’
is CO2 gas, which is used in fire extinguishers.
99. a. The blue colour of crystals of a substance on b. NaHCO 3 (s) + HCl (aq) $ NaCl (aq) + H 2 O (l) + CO 2 (g)
heating in a closed test tube gets changed but the
colour was regained after sometime on cooling. 103. “Sodium hydrogen carbonate is a basic salt.” Justify
Name that substance and write its chemical the statement. How is it converted into washing soda?
formula. Explain the phenomenon involved. Explain.
b. Write name and chemical formulae of two such Ans : [CBSE 2012]
compounds whose one unit is associated with 10 NaHCO3 is a salt of NaOH which is a strong base and
and 2 water molecules respectively. H2CO3 (Carbonic acid) which is a weak acid, therefore
Ans : [CBSE 2015] it is a basic salt. It can be converted into washing soda
a. Hydrated copper sulphate, CuSO4.5H2O is the by heating followed by crystallisation:
Heat
name and chemical formula of that substance. 2NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g) + H 2 O (l)
It loses water of crystallisation on heating and Na2 CO3 + 10H2 O $ Na 2 CO 3 $ 10H 2 O
(washing soda)
regains these molecules of water on exposure to
the atmosphere: 104. Describe an activity with diagram to illustrate that
CuSO 4 $ 5H 2 O
Heat
CuSO 4 + 5H 2 O the reaction of metal carbonates or metal bicarbonates
Blue (Dirty while)
 with acid produces carbon dioxide. Write the relevant b. D is strongly alkaline,
equations of all the reactions that take place. Name c. ‘C’ is strongly acidic,
any two forms in which calcium carbonate is found in d. A is weakly acidic,
nature. e. ‘E’ is weakly basic. D<E<B<A<C is the
Ans : [CBSE 2012] increasing order of H+ ion concentration.
Activity: To show reaction of metal carbonates and 107. You have been provided with three test tubes. One
metal hydrogen carbonates with dilute acids. of them contains distilled water and the other two
1. Take marble chips in Woulfe bottle. contains an acidic solution and a basic solution
2. Set the apparatus as shown in the diagram. respectively. If you are given only red litmus, how will
3. Add dilute HCl with the help of thistle funnel. you identify the contents 5 of each test tube?
4. Collect the gas and pass through lime water and Ans : [CBSE 2011 ]
bring a burning matchstick near the gas.
5. Observe what happens. Add red litmus to each of them. The test tube in
Observation: Lime water turns milky. The burning which it turns blue contains the base.
matchstick gets extinguished. Add blue litmus to the remaining two test tubes.
Conclusion: Metal carbonates react with dilute acids The one in which it turns red contains the acid. The
to liberate carbon dioxide. other one in which blue litmus and red litmus do not
Repeat the experiment with NaHCO3 taken in change contains distilled water,
Woulfe bottle.
Observation: 108. While constructing a house, a builder selects marble
CO2 gas will be evolved which turns lime water milky. flooring and marble table top for the kitchen where
Conclusion: Metal hydrogen carbonates give CO2 with vinegar and lemon juice, tamarind etc., and more
dilute acids. often used for cooking are to be kept. Will you agree
to this selection and why?
Ans : [CBSE 2010]
No, he has taken wrong decision. Marble will react
with vinegar and other acids and get corroded.
CaCO 3 + 2CH 3 COOH $ (CH 2 COO) 2 Ca + H 2 O + CO 2

109. Name the products formed in each case when:

a. Hydrochloric acid reacts with caustic soda.
b. Granulated zinc reacts with caustic soda.
c. Carbon dioxide is passed through lime water.
Ans : [CBSE 2009]
a. NaOH + HCl $ NaCl + H 2 O
Sodium chloride Water

b. Zn + 2NaOH $ Na 2 ZnO 2 + H 2 (g)

soudium zincate Hydrogen
c. Ca (OH) 2 + CO 2 (g) $ CaCO 3 (s) + H 2 O (l)
NaHCO3 + HCl $ NaCl + H2O + CO2 Calcium carbonate Water

Na2CO3 + 2HCl $ 2NaCl + H2O + CO2

105. What is neutralisation reaction? Give two examples. FIVE MARKS QUESTIONS
Ans : [CBSE 2011]
The reaction in which acid reacts with base to form
110. a.Define indicator. Name two indicators obtained
salt and water is called neutralisation reaction e.g.,
from plants.
NaOH + HCl $ NaCl + H2O
b. Write a balanced chemical equation for the
2KOH + H2SO4 $ K2SO4 + 2H2O
reaction taking place when sodium oxide reacts
CaCO3 (Marble), CaCO3(Chalk) are the two forms in
with water. How will this solution behave towards
which calcium is found in nature.
phenolphthalein and red litmus paper?
106. Five solutions A, B, C, D, and E showed pH as 4, 7, c. State what happens when sodium hydroxide
1, 11 and 9 respectively when tested with universal solution reacts with hydrochloric acid.
indicator. Which solution is Ans : [CBSE 2016]
a. Neutral, a. Indicator is a substance which give different
b. Strongly alkaline, colour or odour in acid and base e.g., litmus and
c. Strongly acidic, turmeric are indicators obtained from plants.
d. Weakly acidic, b. Na2O(s) + H2O(l) $ 2NaOH(aq)
e. Weakly alkaline. Solution will turn phenolphthalein pink and red
Arrange the pH in increasing order of H+ ion litmus paper blue.
concentration. c. Sodium chloride and water are formed:
Ans : [CBSE 2011] NaOH(aq) + HCl(aq) $ NaCl(aq) + H2O(l)
a. ‘B’ is neutral,
111. State the reason for the following statements: and H2CO3 is added in test tube ‘B’ in equal amounts:
a. Tap water conducts electricity whereas distilled a. Identify the test tube showing vigorous reaction.
water does not. b. Give reason to support your answer.
b. Dry hydrogen chloride gas does not turn blue c. Name the gas liberated in both the test tubes.
litmus red whereas dilute hydrochloric acid does. How will you prove its liberation?
c. During summer season, a milkman usually adds a d. Write chemical equations for both the reactions.
very small amount of baking soda to fresh milk. e. Out of two acids taken above, which one will have
d. For dilution of an acid, acid is added to water and lower pH value and lower H+ ion concentration
not water to acid. respectively?
e. Ammonia is a base but it does not contain Ans : [CBSE 2014]
hydroxyl group.
a. ‘A’ will show vigorous reaction.
Ans : [CBSE 2015] b. H2SO4 is a strong acid, it reacts faster than H2CO3,
a. Tap water contains ions which makes it a good a weak acid.
conductor whereas distilled water does not contain c. H2 gas. If we bring a burning splinter near the gas,
any ions. it will burn with ‘pop’ sound.
b. Dry HCl gas does not dissociate into ions, so it d. Mg + H2SO4 $ MgSO4 + H2
has no effect on the litmus. Hydrochloric acid Mg + H2CO3 $ MgCO3 + H2
form ions, so it turns blue litmus red. e. H2SO4 will have lower pH. H2CO3 will have lower
c. Baking soda prevents the formation of lactic acid H+ ion concentration,
when milk turns sour.
d. Acid is added to water slowly because the reaction 115. Write chemical equations when zinc granules react
is highly exothermic. If water is added to acid, with
then glass container may break due to lot of heat a. Sulphuric acid,
evolved. b. Hydrochloric acid,
e. NH3 dissolves in H2O forming NH4OH, therefore c. Aluminium chloride,
it acts as base: d. Sodium hydroxide,
NH3 + H2O $ NH4OH $ NH4 + OH- e. Nitric acid
Ans : [CBSE 2014]
112. a.State the chemical properties on which the
a. Zn(s) + H2SO4(dil.) $ ZnSO4(aq) + H2(g)
following uses of baking soda are based:
b. Zn(s) + 2HCl(dil) $ ZnC(aq) + H2(g)
(i) as an antacid,
c. Zn(s) + AlCl3(aq) $ No reaction
(ii) as a soda acid fire extinguisher,
d. Zn(s) + 2NaOH(aq) $ Na2ZnO2(aq) + H2(g)
(iii) to make bread and cake soft and spongy.
e. 3Zn (s) + 8HNO 3 (dil) $ 3Zn (NO 3) 2 (aq) + 2NO (g) + 4H 2 O (l)
b. How is washing soda obtained from baking soda?
Write the relevant balanced chemical equation. 116. The metal salt ‘A’ is blue in colour. When salt ‘A’ is
Ans : [CBSE 2015] heated strongly over a burner, then a substance ‘B’
a. (i) It is basic in nature. present in it is eliminated and a white powder ‘C’ is
(ii) It liberates CO2 with acid which extinguishes left behind. When a few drops of a liquid ‘D’ is added
fire. to powder ‘C’, it becomes blue again.
(iii) It releases CO2 gas on heating which makes a. Identify A, B, C and D.
bread and cake soft and spongy. b. Write the chemical equations involved.
b. Washing soda is obtained by heating baking soda c. Give an example of the salt which also shows the
followed by crystallisation: above property.
2NaHCO3(s) $ Na2CO3 + CO2 + H2O Ans : [CBSE 2014]
Na 2 CO 3 + 10H 2 O $ Na 2 CO 3 $ 10H 2 O a. ‘A’ is CuSO4.5H2O, ‘B’ is H2O, ‘C’ is CuSO4
(Washing
(Washing soda)
soda)
(ahydrous).
Heat
113. Write balanced chemical equations for the following: b. CuSO 4 $ 5H 2 O (s) CuSO 4 (s) + H 2 O (l)
(Blue)
a. Bleaching powder is kept open in air. (White) B

b. Blue crystals of copper sulphate are heated. c. FeSO4.7H2O is a salt which also shows this
c. Chlorine gas is passed through dry slaked lime. property.
d. Carbon dioxide gas is passed through lime water.
e. NaOH solution is heated with zinc granules. 117. a.Write the chemical name and chemical formula of
Ans : [CBSE 2014] washing soda.
b. How is chlorine obtained from sodium chloride?
a. CaOCl2 + CO2 $ CaCO3 + Cl2
Heat Give equations for the reactions involved.
b. CuSO4.5H2O CuSO4 + 5H2O c. Give an example of the salt which also shows the
c. Ca(OH)2 + Cl2 $ CaOCl2 + H2O above property.
d. Ca(OH)2 + CO2 $ CaCO3 + H2O
Ans : [CBSE 2014]
e. Zn + 2NaOH $ Na2ZnO2 + H2
a. Na 2 CO 3 $ 10H 2 O , Sodium carbonate decahydrate.
114. Equal length of magnesium ribbon are taken in two b. NaCl + H 2 O + NH 3 + CO 2 $ NaHCO 3 + NH 4 Cl
test tubes A and B. H2SO4 is added to test tube ‘A’ Heat
2NaHCO 3 Na 2 CO 3 + H 2 O + CO 2
 Na 2 CO 3 + 10H 2 O $ Na 2 CO 3 $ 10H 2 O relevant chemical equation.
CO2 gas is passed through ammonical brine to get (b) While diluting an acid, why is it recommended
back NaHCO3. NaHCO3 on heating again gives that the acid should be added to water and not
Na2CO3 which on crystallisation gives washing water to the acid?
soda. Ans : [CBSE 2012]
c. Na2CO3 is salt of NaOH (Strong base) and
a. ‘X’ is NaOH. It is a base which is hygroscopic
H2CO3(Weak acid), therefore it is a basic salt. It
i.e., absorbs moisture from the atmosphere and
is used for softening hard water.
turns sticky. It is also formed by the electrolysis of
118. a.Identify the acid and the base whose combination aqueous solution of brine by chlor alkali process:
Heat
forms the common salt that you use in your food. 2NaCl (aq) + 2H 2 O (l) 2NaOH (aq) + H 2 (g
Write its chemical formula and chemical name of Neutralisation reaction will take place between
the salt. NaOH and HCl:
b. What is rock salt? Mention its colour and the NaOH + HCl $ NaCl + H2O
reason due to which it has this colour. b. It is because the process is highly exothermic. If
c. What happens when electricity is passed through we add H2O to acid, the glass container may break
brine? Write chemical equation for it. due to excess heat evolved.
Ans : [CBSE 2013] 121. a.Explain the following chemical properties of acids
a. NaOH (Sodium hydroxide) and HCl (Hydrochloric with the help of balanced chemical equations only:
acid) form common salt. NaCl is common salt, (1) when an acid reacts with a metal carbonate,
sodium chloride. (2) when an acid reacts with a metal bicarbonate,
b. Rock salt is sodium chloride found in the form of (3) when an acid reacts with a metal oxide.
rocks. It is yellowish in colour due to the presence b. You are given three solutions A, B and C with pH
of impurities. values, 2,10 and 13 respectively. Which solution
c. Sodium hydroxide, H2 gas and chlorine gas will has the highest hydrogen ion concentration among
be formed: the three and state the nature ‘acidic or basic’ of
2NaCl (aq) + 2H 2 O (l) $ 2NaOH (aq) + H 2 (g) + Cl 2 (g) each solution.
Ans : [CBSE 2012]
119. a.Explain why is hydrochloric acid a strong acid and
acetic acid, a weak acid. How can it be verified? a. (1)Na2CO3 + H2SO4(dil) $ Na2SO4 + H2O + CO2
b. Explain why aqueous solution of an acid conducts (2) 2NaHCO3 + H2SO4(dil) $ Na2SO4+ H2O + CO2
electricity. (3) MgO + H2SO4 $ MgSO4 + H2O
c. You have four solutions A, B, C and D. The pH of b. ‘A’ has more H+ ion concentration among the
solution A is 6, B is 9, C is 12 and D is 7. three.
(1) Identify the most acidic and most basic A’ is acidic.
solutions respectively. ‘B’ is basic.
(2) Arrange the above four solutions in the ‘C’ is strongly basic.
increasing order of H+ ion concentration.
122. a.A metal compound ‘X’ reacts with dilute H2SO4
(3) State the change in colour of pH paper on
to produce effervescence. The gas evolved
dipping in solution C and D.
extinguishes a burning candle. If one of the
Ans : [CBSE 2012] compound formed is calcium sulphate, then what
a. Hydrochloric acid is a strong acid because it is is ‘X’ and the gas evolved? Also write a balanced
completely ionised in its aqueous solution. Acetic chemical equation for the reaction which has
acid is only partially ionised. HCl reacts with occurred.
Mg vigorously whereas acetic acid reacts less b. (i) Name one antacid. How does it help to relieve
vigorously. indigestion in stomach?
b. Aqueous solution of acid contain ions which carry (ii) A farmer treats the soil with quicklime or
current, it conducts electricity. calcium carbonate. What is the nature of the
c. (1) With pH = 6 ‘A’ is most acidic, soil? Why does the farmer treat the soil with
With pH = 12, ‘C’ is most basic. quicklime?
(2) C < B < D < A is the increasing order of H+ Ans : [CBSE 2012]
ion concentration.
This is is calcium carbonate
(3) pH paper will turn blue in ‘C’ with pH = 12,
CaCO 3 (s) + H 2 SO 4 (dill) $ CaSO 4 (aq) + H 2 O (l) + CO 2 (g)
basic pH paper will turn green in D with pH
The gas evolved is carbon dioxide (CO2).
= 7, neutral.
b. (i) NaHCO3(baking soda) is an antacid. If
120. (a) Dry pellets of a base ‘X’ when kept in open neutralises excess of HCl in stomach and
absorbs moisture and turns sticky. The compound gives relief.
is also formed by chlor-alkali process. Write the (ii) The nature of soil is acidic. The farmer treats
chemical name and formula of X. Describe chlor- the soil with quicklime (basic in nature) to
alkali process with balanced chemical equations. neutralise the acidity of soil and make it fit
Name the type of reaction occurs when X is for crops.
treated with dilute hydrochloric acid. Write the
123. a. Tooth enamel is one of the hardest substance in
 our body. Explain the changes in pH of mouth
which indicates tooth decay. How does tooth
paste help in preventing it?
b. What is the nature of salt if pH of its aqueous
solution is greater than 7? Name the acid and
base that would be used to prepare the following
salts:
(i) Potassium sulphate, (ii) Ammonium chloride
Ans : [CBSE 2012]
a. Tooth enamel is made up of Ca3(PO4)2 calcium
phosphate. pH = 5.5 causes tooth decay because
Ca3(PO4)2 reacts with acid. Tooth paste are basic,
neutralises the acid in mouth and prevents tooth
decay.
b. The salt is basic if pH > 7.
(i) KOH and H2SO4 are needed to prepare K2SO4.
(ii) NH4OH and HCl are needed to prepare
NH4Cl.

124. (a) A salt is produced by reaction between an acid

and a base. Identify the acid and base from which
the following salts have been formed:
(i) Na2SO4, (ii) NH4Cl, (Hi) KNO3, (iv) NaCl
(b) Which one of these will have pH less than 7 and
why?
Ans : [CBSE 2012]
(a) (i) Na2SO4 is prepared from NaOH and H2SO4
(ii) NH4Cl is formed by NH4OH and HCl.
(iii) KNO3 is formed by KOH and HNO3.
(iv) NaOH is formed by NaOH and HCl.
(b) NH4Cl has pH less than 7 because it is a salt of
weak base NH4OH and strong acid, HCl, therefore
the salt is acidic.

125. What are strong acids and weak acids? In the following
list of acids, separate strong acids from weak acids:
hydrochloric acid, citric acid, acetic acid, nitric acid,
formic acid, sulphuric acid.
Ans : [CBSE 2012]
Strong acids are those acids which are completely
ionised in aqueous solution e.g.-,
HCl(aq) $ H+(aq) + Cl- (aq)
Weak acids do not ionise completely in aqueous
solution:
CH3COOH(aq) CH 3 OO- (aq) + H+ (aq)
Strong acids: Hydrochloric acid, Nitric acid, Sulphuric
acid.
Weak acids: Citric acid, Acetic acid, Formic acid.
Chap 1 : Chemical Reactions and Equations www.cbse.online

CHAPTER 1
Chemical Reactions and Equations

ONE MARK QUESTIONS following reaction:

Sodium hydroxide + Sulphuric acid $
Ans : [CBSE 2013]
1. In electrolysis of water, why is the volume of gas
collected over one electrode double that of gas 2NaOH + H2SO4 $ Na2SO4 + 2H2O
collected over the other electrode. 9. Name and state the law which is kept in mind when
Ans : [CBSE S.R 2018, CBSE 2009, 2012, 2013] we balance chemical equations.
Water contains hydrogen and oxygen in the ratio of Ans : [CBSE 2012]
2 : 1, that is why volume of H2 is double than that of Law of conservation of mass. It states Matter can
oxygen. neither be created nor be destroyed. The total mass
2. What can be seen when a strip of copper metal is of reactants must be equal to total mass of products.
placed in a solution of silver nitrate? 10. What is meant by a chemical reaction?
Ans : [CBSE 2015] Ans : [CBSE 2011]
The solution will become blue, shiny silver metal will Chemical reaction, a process in which one or more
get deposited. substances, the reactants, are converted to one or more
Cu(s) + 2AgNO3(aq) $ Cu(NO3)2 (aq) + 2Ag(s) different substances, the products. Substances are
either chemical elements or compounds. A chemical
3. State one industrial application of reduction process.
reaction rearranges the constituent atoms of the
Ans : [CBSE 2015] reactants to create different substances as products
It is used in the extraction of metals e.g.,
Heat 11. AgNO3(aq) + NaCl(aq) $ AgCl . + NaNO3(aq)
ZnO(s) + C(s) Zn(s) + CO2(g)
FeS + H2SO4 $ FeSO4 + H2S -
4. Which one of the following is a chemical change? Give Consider the above mentioned two chemical equations
reason also. with two different kinds of arrows (- and . ) along
(a) Burning of wax (b) Melting of wax with the product. What do these two different arrows
Ans : [CBSE 2014] indicate?
Ans : [CBSE 2011]
Burning of gas is a chemical change because new
products with new properties will be formed on - shows evolution of gas, . represents a precipitate.
burning.
12. Hydrogen being a highly inflammable gas and
5. Which one is a chemical change: oxygen being a supporter of combustion, yet water, a
Rusting of iron or melting of iron? compound made up of hydrogen and oxygen is used to
Ans : [CBSE 2014] extinguish fire. Why?
Ans : [CBSE 2011]
Rusting of iron is a chemical change.
H2O is a compound constituted of hydrogen of oxygen
6. State one basic difference between a physical change elements and being a compound it has different
and a chemical change. properties as compared to its constituting elements.
Ans : [CBSE 2014, 2011]
13. N2(g) + 3H2(g) $ 2NH3(g), name the type of
In a physical change, no new substance is formed. reaction.
In a chemical change, new substance(s) with new
Ans : [CBSE 2011]
properties is/are formed.
Combination reaction.
7. Name the oxidising and reducing agent in the following
reaction: 14. If copper metal is heated over a flame it develops
a coating. What is the colour and composition of
CuO + H2 $ Cu + H2O
coating?
Ans : [CBSE 2013]
Ans : [CBSE 2011]
CuO is oxidising agent H2 is reducing agent.
Black coloured coating is formed. It is a due to
8. Write a complete balanced chemical equation for the formation of copper oxide.
15. Write a balanced chemical equation to represent It is photochemical decomposition reaction.
the following reaction: carbon monoxide reacts with
hydrogen gas at 340 atm to form methyl alcohol. 25. Write a balanced chemical equation for the reaction
between sodium chloride and silver nitrate indicating
Ans : [CBSE 2011]
the physical state of the reactants and the products.
340 atm
CO(g) + 2H2(g) CH3OH(l) Ans : [CBSE 2010]
Heat
16. Which one is a chemical change: fermentation of fruit AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq)
(Silver Nitrate)
juice or diluting fruit juice? (Sodium Chloride) (Silver Chloride) (Sodium NItrate)

Ans : [CBSE 2011] 26. Complete and balance the following equation:
Fermentation of fruit juice is a chemical change. Fe2O3 + Al $
Ans : [CBSE 2010]
17. Is burning of a candle wax a physical or a chemical
change? Fe2O3 + 2Al $ 2Fe + Al2O3
Ans : [CBSE 2011] 27. Balance the following chemical equation:
Burning of a candle wax is a chemical change. Pb(NO3)2 $ PbO + NO2 + O2
Ans : [CBSE 2009]
18. Write a balanced equation for the chemical reaction
that can be characterised as precipitation reaction. 2Pb(NO3)2 Heat 2PbO + 4NO2 + O2
Ans : [CBSE 2011] 28. Identity the type of reaction in the following example:
AgNO3(aq) + NaCl(aq) $ AgCl(s) + NaNO3(aq) Na2SO4(aq) + BaCl2(aq) $ BaSO4(s) + 2NaCl(ag)
It is a precipitation reaction. Ans : [CBSE 2008(C)]
19. State the main difference between endothermic Double displacement reaction.
reaction and an exothermic reaction.
29. Identify the type of reaction in the following example:
Ans : [CBSE 2011] Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s)
In endothermic reaction, heat is absorbed. In Ans : [CBSE 2008(C)]
exothermic reaction, heat is evolved.
Displacement reaction.
20. What happens chemically when quick lime is added to
30. Identify the type of reaction in the following example:
water filled in a bucket?
2H2(g) + O2(g) $ 2H2O(l)
Ans : [CBSE 2010, 2008]
Ans : [CBSE 2008(C)]
Calcium hydroxide (Slaked lime) is formed with
Combination reaction.
evolution of heat and hissing sound.
CaO(s) + H2O(l) $ Ca(OH)2(aq) 31. Balance the given chemical equation:
Al(s) + CuCl2(aq) $ AlCl3(aq) + Cu(s)
21. Define oxidation and reduction.
Ans : [CBSE 2008(C)]
Ans : [CBSE 2011, 2010]
2Al(s) + 3CuCl2(aq) $ 2AlCl3(aq) + 3Cu(s)
Oxidation is a process in which oxygen is added or
loss of electrons take place. Reduction is a process in 32. Balance the given chemical equation:
which hydrogen is added or gain of electrons takes FeSO4(s)
Heat
Fe2O3(s) + SO2(g) + SO3(g)
place.
Ans : [CBSE 2008]
22. Give an example of double displacement reaction 2FeSO4(s)
Heat
Fe2O3(s) + SO2(g) + SO3(g)
(only with complete balanced equation).
Ans : [CBSE 2011, 2010] 33. Balance the following chemical equation:
Fe(s) + H2O(g) $ Fe3O4(s) + H2(g)
BaCl2(aq) + H2SO4(dil.) $ BaSO4(s) + 2HCl(aq)
It is a double displacement reaction. Ans :
3Fe(s) + 4H2O(g) $ Fe3O4(s) + 4H2(g)
23. On what basis is a chemical reaction balanced?
Ans : [CBSE 2010, 2008] 34. On adding dilute hydrochloric acid to copper oxide
powder, the solution formed is blue green. Predict the
Chemical equation is balanced on the basis of law of
new compound formed which imparts a blue green
conservation of mass.
colour to the solution.
24. What change in colour is observed when white silver Ans : [CBSE 2008]
chloride is left exposed to sun¬light? State the type of CuO + 2HCl $ CuCl2 + 2H2O
chemical reaction in this change. Copper chloride solution imparts blue green colour to
Ans : [CBSE 2010, 2009] the solution.
Grey coloured silver metal is formed and pungent
35. Why is respiration considered as exothermic process?
smelling chlorine gas is evolved.
sunlight Ans : [CBSE 2008]
2AgCl(s) 2Ag(s) + Cl2(g)
 Respiration is an exothermic process because energy is collected by the method as shown in figure.
is given out in respiration.

TWO MARKS QUESTIONS

36. Write the essential condition for the following reaction

to take place:
2AgBr $ 2Ag + Br2
Write application of this reaction.
Ans : [CBSE 2016]
The reaction will take place in presence of sunlight.
This reaction is used in black and white photography.
Answer the following questions:
37. (a) Complete the following equation for the chemical a. Name the gas liberated.
reaction: b. Name the method used for collection of gas.
Heat c. Is the gas soluble or insoluble in water?
FeSO4(s) Fe2O3 + ___ +___
d. Is the gas lighter or heavier than air?
(b) What happens when water is added to quicklime
(CaO)? Write the chemical equation. Ans : [CBSE 2015, CBSE 2010]
Ans : [CBSE 2016] a. The gas liberated is H2.
Heat b. It is collected by downward displacement of water.
(a) 2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g)
c. The gas is insoluble in water.
(b) Slaked lime Ca(OH)2 is formed. Hissing sound and
d. Hydrogen gas is lighter than air.
lot of heat is also produced:
CaO(s) + H2O(l) $ Ca(OH)2(aq) 43. Giving an example list two important information
which makes a chemical equation more useful
38. Write balanced chemical equation for the following (informative).
reactions: Ans : [CBSE 2015]
a. Hydrogen sulphide burns in air to give water and
sulphur dioxide. a. It should include physical states of reactants and
b. Barium chloride reacts in aqueous solution with products.
zinc sulphate to give zinc chloride and barium b. It should specify conditions under which reaction
sulphate. takes place e.g.,
Ans : [CBSE 2016] 2Na(s) + 2H2O(l) $ 2NaOH(aq) + H2(g)
(Cold)
a. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g) sunlight
H2(g) + Cl2(g) 2HCl(g)
b. BaCl(aq) + ZnSO(aq) $ BaSO4 (s) + ZnCl2(aq)
44. Consider the following chemical equation:
39. List two observations that are noticed when an iron
X + Barium chloride $ Y + Sodium chloride
nail is put inside copper sulphate solution. Write the (White ppt)
chemical equation for the reaction that occurs. Identify (a) X and Y (b) The type of reaction.
Ans : [CBSE 2016] Ans : [CBSE 2015]
The blue coloured solution will become pale green. (a) X is silver nitrate, Y is silver chloride.
Reddish brown metal will get deposited. 2AgNO 3 (aq) + BaCl 2 (aq) $ 2AgCl . + Ba (3NO 3) 2 (aq)
Fe (s) + CuSO 4 (aq) $ FeSO 4 (aq) + Cu (s) (White ppt)

(Blue) (Pale Green) (Reddish brown) (b) The reaction is an example of double displacement
40. Name the reducing agent in the following reaction: (precipitation) reaction.
3MnO2 + 4A1 $ 3Mn + Al2O3
State which is more reactive, Mn or Al and Why? 45. (a) Write a balanced chemical equation for the process
of photosynthesis.
Ans : [CBSE 2016, 2015]
(b) When do desert plant take up carbon dioxide and
Al is the reducing agent. Al is more reactive than Mn. perform photosynthesis.
Reason: It is because Al is displacing Mn from MnO2. Ans : [CBSE 2015]
sunlight
41. “We need to balance a skeleton chemical equation”. a. 6CO2(g) + 6H2O(l) chlorophyll C6H12O6(aq) + 6O2(g)
Give reason to justify the statement. b. Desert plant take up carbon dioxide and perform
Ans : [CBSE 2015] photosynthesis at night.
We must balance a skeletal equation so as to ensure 46. Two reactions are given below:
that the reaction follows ‘Law of conservation of mass’. a. 2KI + Cl2 $ 2KCl + I2
The total mass of reactants must be equal to the total b. 2K + Cl2 $ 2KCl
mass of products, that is why all reactions should he Identify the type of reaction, giving justification in
balanced. each case.
42. A metal is treated with dilute H2SO4. The gas evolved Ans : [CBSE 2015]
 a. Displacement reaction because Cl2 is displacing I2 answer the questions which follow:
Heat
from KI solution. (i) CuO + H2 Cu + H2O
b. Combination reaction because K reacts with Cl2 (ii) ZnO + C
Heat
Zn + CO
to form potassium chloride. a. Name the substances that are oxidised and
reduced respectively in each case,
47. On heating copper powder in air, the surface of copper
b. Identify the reducing agent in each case.
powder becomes coated with black CuO. How can this
black coating be converted into brown copper? Write Ans : [CBSE 2013]
chemical equation for the reaction that occurs during a. H2 is getting oxidised to H2O, CuO getting reduced
the colour change. to Cu.
Ans : [CBSE 2015] b. H2 is reducing agent in (i) reaction whereas C is
Heat reducing agent in second reaction.
2Cu + O2 2CuO
(Black)
54. What is a redox reaction? Identify the substances
Copper oxide on heating with H2 will change back to
oxidised and the substance reduced in the following
reddish brown copper metal.
Heat reactions:
CuO(s) + H2(g) Cu(s) + H2O(g) a. MnO2+ 4HCl $ MnCl2 + Cl2 + H2O
48. What is observed when a solution of potassium iodide b. CuO + H2 $ Cu + H2O
is added to a solution of lead nitrate? Name the type Ans : [CBSE 2012]
of reaction. Write a balanced chemical equation to Redox reaction is a reaction in which oxidation and
represent the above chemical reaction. reduction takes place simultaneously.
Ans : [CBSE 2014, 2013] c. HCl is the substance oxidised, MnO2 is the
Yellow precipitate is formed due to formation of lead substance getting reduced.
iodide. d. H2 is getting oxidised, CuO is getting reduced.
It is a precipitation as well as double displacement 55. Write balanced chemical equations for the following
reaction. reactions:
Pb (NO 3) (aq) + 2KI (ag) $ PbI 2 (s) + 2KNO 3 (aq) a. Silver bromide on exposure to sunlight decomposes
Yellow ppt

49. Write a balanced chemical equation for the process of into silver and bromine.
photosynthesis and the conditions of reaction giving b. Sodium metal reacts with water to form sodium
physical state of all substances. hydroxide and hydrogen gas.
Ans : [CBSE 2014) Ans : [CBSE 2012]
sunlight
6CO 2 (g) + 6H 2 O (l)
sunlight
C 6 H 12 O 6 (aq) + 6O 2 (g) a. 2AgBr(s) 2Ag(s)+ Br2(g)
chlorophy II
b. 2Na(s) + 2H2O(l) $ 2NaOH(l) + H2(g)
50. Give one example of each:
a. Chemical reaction showing evolution of a gas. 56. Identify the type of reaction from the following
b. Change in colour of a substance during chemical equations:
reaction. a. CH4 + 2O2 $ CO2 + 2H2O
b. Pb(NO3)2 + 2KI $ PbI2 + 2KNO3
Ans : [CBSE 2013]
c. CaO + H2O $ Ca(OH)2
a. 2K(s) + 2H2O(l) $ 2KOH(aq) + H2(g) d. CuSO4 + Zn $ ZnSO4 + Cu
Heat
b. FeSO4.7H2O(aq) FeSO4(s) + 7H2O(l) Ans : [CBSE 2012]
(Pale green) (Dirty white)
a. Oxidation reaction
51. Translate the following statement into chemical b. Double displacement reaction
equation and then balance it. “A metal in the form of c. Combination reaction
ribbon burns with a dazzling white flame and changes d. Displacement reaction
into white powder.”
Ans : [CBSE 2013] 57. Write balanced equation for the reaction between Mg
Burning
and hydrochloric acid. Name the product obtained,
2Mg(s) + O2(g) 2MgO(s) + Light + Heat identify the type of reaction.
52. It has been found that marble of Taj is getting corroded Ans : [CBSE 20i2]
due to development of industrial areas around it. Mg(s) + 2HCl(dil) $ MgCl2(aq) + H2(g)
Explain this fact giving a chemical equation. Magnesium chloride and hydrogen gas are formed in
Ans : [CBSE 2013] this reaction. It is a displacement reaction.
Taj is made up of CaCO3 which reacts with acid 58. a. What is colour of ferrous sulphate crystals? How
formed by pollution of SO2(g) and NO2 from Mathura does this colour change after heating?
refinery and other industries. b. Name the products formed on strongly heating
CaCO3 + 2H2SO4 $ CaSO4 + CO2 + 2H2O ferrous sulphate crystals. What type of chemical
CaCO3 + 2HNO3 $ Ca(NO3)2 + H2O + CO2 reaction occurs in this change?
53. Consider the chemical equations given below and Ans : [CBSE 2012.2009]
a. FeSO 4 $ 7H 2 O crystals are pale green in colour.
 They become dirty white on heating. 64. Translate the following statements into chemical
b. Ferric oxide, sulphur dioxide and sulphur trioxide equations and then balance them:
are formed: a. Hydrogen gas combines with nitrogen to form
Heat
2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g) ammonia.
It is a decomposition reaction. b. Hydrogen sulphide gas burns in air to give water
and sulphur dioxide.
59. Reaction of compound X with aluminium is used to c. Barium chloride reacts with aluminium sulphate
join railway tracks or cracked machine parts. to give aluminium chloride and a precipitate of
a. Identify the compound. barium sulphate. State the two types in which
b. Name the reaction. this reaction can be classified.
c. Write a balanced chemical equation for the d. Potassium reacts with water to give potassium
reaction. hydroxide and hydrogen gas.
Ans : [CBSE 2012] Ans : [CBSE 2012]
a. The compound X is Fe2O3 (Ferric oxide) or Iron a. 3H2(g) + N2(g) $ 2NH3(g)
(III) oxide. b. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g)
b. It is called Thermite Reaction. c. 3BaCl 2 (aq) + Al 2 (SO 4) 3 (aq) $ 3BaSO 4 (s) + 2AlCl 3 (aq)
Heat
c. 2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l) This reaction can be classified as a double
displacement reaction as the two reacting species
60. Using balanced chemical equation explain the (BaSO4, Al2SO4)3 undergoes mutual exchange
difference between a displacement reaction and a of ions. It can also be classified as precipitation
double displacement reaction. reaction, since a white ppt. of BaSO4 is obtained.
Ans : [CBSE 2012, 2011] d. 2K(s) + 2H2O(l) $ 2KOH(aq) + H2(g)
Displacement reaction: A reaction in which a more
65. When a metal X is added to salt solution of metal Y,
reactive element displaces a less reactive element from
the following chemical reaction takes place:
its salt solution e.g.,
2KBr(aq) + Cl2(g) $ 2KCl(aq) + Br2(aq) Metal X + Salt solution of Y $
Double displacement reaction: A reaction in which Salt solution of X + Metal Y
two compounds exchange their ions to form two new Mention the inference you draw regarding the
compounds e.g., reactivity of metal X and Y and also the type of
KOH + HNO3 $ KNO3 + H2O reaction. State the reason of your conclusions.
61. Give an example each for thermal decomposition Ans : [CBSE 2012]
and photochemical decomposition reactions. Write X is more reactive than Y because , X displaces Y from
balanced chemical equation also. its salt solution. Hence, this reaction is an example of
Ans : [CBSE 2012] displacement reaction.
Thermal decomposition: 66. Identify the type of each of the following reactions:
Heat
ZnCO3(s) ZnO(s) + CO2(g) a. A reaction in which a single product is formed
Photochemical decomposition: from two or more reactants.
sunlight
2AgI(s) 2Ag(s) + I2(g) b. The reaction mixture becomes warm.
c. An insoluble substance is formed.
62. Why are decomposition reactions called the opposite d. External surface of the container in which reaction
of combination reactions? Give chemical equations for takes place becomes cold.
these reactions. Ans : [CBSE 2012]
Ans : [CBSE 2012]
a. Combination reaction
In decomposition reactions, a compound is broken b. Exothermic reaction
down into one or more elements or compounds e.g., c. Precipitation reaction (Double displacement
Heat
CaCO3(s) CaO(s) + CO2(g) reaction)
In combination reactions, two or more elements d. Endothermic reaction
or compounds combine to form a new compound.
Therefore, decomposition reactions are opposite to 67. A solution of potassium chloride when mixed with
combination reactions e.g., silver nitrate solution, an insoluble white substance is
3Mg(s) + N2(g)
Burns
Mg3N2(s) formed. Write the chemical reaction involved and also
mention the type of reaction.
63. Why does the colour of copper sulphate solution Ans : [CBSE 2012, 2011, 2010]
changes when an iron pin is dipped in it?
AgNO3(aq) + KCl(aq) $ AgCl(s)+KNO3(aq)
Ans : [CBSE 2012] (White ppt.)

It is a double displacement reaction.

Iron being more reactive displaces copper from copper
sulphate (Blue) solution to form iron (II) sulphate 68. Using a suitable chemical equation justify that some
(Pale green) solution and reddish brown copper metal chemical reactions are determined by
gets deposited. a. Change in colour.
Fe(s) + CuSO4 $ FeSO4(aq) + Cu(s) b. Change in temperature.
 Ans : [CBSE 2011] fumes and a white residue is left behind.
a. Change in colour: Blue coloured crystalline a. Name the salt.
copper sulphate crystals changes to white CuSO4 b. Write the equation for the decomposition reaction.
(anhydrous) on heating. Ans : [CBSE 2011]
Heat
CuSO4.5H2O CuSO4 + 5H2O a. Lead nitrate
(Blue) (Dirty white) Heat
b. 2Pb (NO 3) 3 (s) 2PbO (s) + 4NO 2 (g) + O 2 (g)
b. Change in temperature: (White) (Residue) (Brown)
CaO(s) + H2O(l) $ Ca(OH)2(aq) + Heat 74. When a solution of potassium iodide is added to a
solution of lead nitrate in a test tube, a reaction takes
69. (a) A solution of substance X is used for white
place.
washing. What is substance X? Write the chemical
a. What type of reaction is this?
reaction of X with water.
b. Write the balanced chemical equation to represent
(b) Why does the colour of copper sulphate solution
the above reaction.
changes when iron nail is dipped in it?
Ans : [CBSE 2011, 2010, 2008]
Ans : [CBSE 2011]
a. It is precipitation as well as double displacement
a. X is CaO, calcium oxide
reaction.
CaO(s) + H2O(l) $ Ca(OH)2(aq)
b. Pb (NO 3) (aq) + 2KI (aq) $ Pbl 2 (s) + 2KNO 3 (aq)
b. It is because Fe displaces Cu from CuSO4 (blue)
solution to form FeSO4 (pale green) and reddish 75. Define combination reaction. Give one example of a
brown Cu metal gets deposited. combination reaction which is also exothermic.
70. Balance the following reactions: Ans : [CBSE 2011]
a. BaCl2 + H2SO4 $ BaSO4 + HCl Combination reaction: The reaction in which two
b. Ca(OH)2 + HNO3 $ Ca(NO3)2 + H2O or more elements or compounds combine to form
c. Pb(NO3)2 $ PbO + NO2 + O2 compound(s) e.g.,
d. MnO2 + HCl $ MnCl2 + Cl2 + H2O C(s) + O2(g) $ CO2(g) + Heat
Ans : [CBSE 2011, 2009, 2008, 2008C] It is an exothermic, combination reaction.
a. BaCl 2 (aq) + H 2 SO 4 (dil) $ BaSO 4 (s) + 2HCl (aq) 76. What happens when an aqueous solution of sodium
b. Ca (OH) 2 (aq) + 2HNO 3 $ Ca (NO 3) 2 (aq) + 2H 2 O (l) sulphate reacts with an aqueous solution of barium
Heat
c. 2Pb (NO 3) 2 (s) 2PbO (s) + 4NO 2 (g) + O 2 (g) chloride? State the physical conditions of reactants in
d. MnO 2 + 4HCl $ MnCl 2 + Cl 2 + 2H 2 O which the reaction between them will not take place.
Write the balanced chemical equation for the reaction
71. Write the balanced equation for the following reactions and name the type of reaction.
and identify the type of reaction in each case: Ans : [CBSE 2016, 2010]
a. Potassium bromide + Barium iodide $ White precipitate of BaSO4 is formed.
Barium bromide + Potassium Iodide BaCl 2 (aq) + Na 2 SO 4 (aq) $ BaSO 4 (s) + 2NaCl (aq)
b. Hydrogen(g) + Chlorine(g) $ Hydrogen It is a double displacement reaction. If reactants are
chloride(g) taken in solid state, products will not be formed.
Ans : [CBSE 2011]
77. What is redox reaction? When a magnesium ribbon
a. 2KBr(aq) + BaI2 $ BaBr2(aq) + 2KI(aq) burns in air with a dazzling flame and forms a white
It is double displacement reaction. ash, is magnesium oxidised or reduced. Why?
sunlight
b. H2(g) +. Cl2(g) 2HCl(g) Ans : [CBSE 2010, 2009]
It is combination reaction.
Redox reaction is a reaction in which oxidation and
72. A zinc plate was put into solution of copper sulphate reduction takes place simultaneously.
kept in a glass container. It was found that blue colour Mg is getting oxidised because it is gaining oxygen
of the solution gets fader and fader with passage of to form magnesium oxide.
time. After few days when zinc plate was taken out of
the solution, a number of holes were observed on it. 78. Write any two observations in an activity which may
a. State the reason for the changes observed on zinc suggest that a chemical reaction has taken place. Give
plate. an example in support of your answer.
b. Write the chemical equation for the reaction Ans : [CBSE 2010]
involved.
a. Change in colour:
Ans : [CBSE 2011] AgNO 3 (aq) + KI (aq) $ AgI (s) + KNO 3 (aq)
(Yellow ppt)
a. Zinc displaces copper from copper sulphate
solution to form colourless ZnSO4 and copper b. Evolution of gas:
metal is deposited. Zinc gets consumed due to Zn(s) + H2SO4(aq) $ ZnSO4 (aq) + H2(g)
which holes are formed. 79. When the powder of common metal is heated in open
b. Zn(s) + CuSO4(aq) $ ZnSO4(aq) + Cu(s) china dish its colour turns black. However, when
73. A white salt on heating decomposes to give brown
hydrogen is passed over the hot black substance so
formed, it regains its original colour. Based on the
 above information answer the following questions: Oxidation reaction: The reaction in which O2 is added
a. What type of chemical reaction takes place in or H2 is removed or loss of electrons takes place is
each of the two given steps? called oxidation reaction. E.g.,
b. Name the metal initially taken in powdered form. 2Cu(s) + O2(g) $ 2CuO(s)
Write balanced equations for both the reactions. It is an exothermic reaction.
Ans : [CBSE 2010]
a. Oxidation reaction, Redox reaction THREE MARKS QUESTIONS
b. Copper metal was present initially
Heat
2Cu (s) + O 2 (g) CuO (s)
(Black) 85. Decomposition reactions require energy either in the
Heat
CuO (s) + H 2 (g) Cu (s) + H 2 O (l) form of heat, light or electricity for breaking down the
(Reddish brown)
reactants. Write an equation each for decomposition
80. Why do we store silver chloride in dark coloured reactions where energy is supplied in the form of heat,
bottle? Explain in brief. light and electricity.
Ans : [CBSE 2010] Ans : [CBSE 2018, 2014]
It is done so as to cut off the exposure to sunlight. a. CaCO3(s)
Heat
CaO(s) + CO2(g)
AgCl is photosensitive, it will decompose to Ag and sunlight
b. 2AgBr(s) 2Ag(s) + Br2(g)
Cl2 in the presence of sunlight. Electricity
sunlight c. 2H2O(l) 2H2(g) + O2(g)
2AgCl(s) 2Ag(s) + Cl2( g)
86. In the electrolysis of water:
81. “Oxidation and reduction processes occur
a. Name the gas collected at the cathode and anode
simultaneously”. Justify this statement with the help
respectively.
of example.
b. Why is volume of gas collected at one electrode
Ans : [CBSE 2010] double than that at the other? Name this gas.
Oxidation involves loss of electrons or addition of c. How will you test this gas?
oxygen. Whereas reduction involves gam of electrons Ans : [CBSE 2012, CBSE Sample Paper 2018]
or addition of hydrogen e.g.,
a. Hydrogen is collected at the cathode, oxygen is
collected at the anode.
b. It is because H2O contains hydrogen and oxygen
in the ratio 2 : 1.
c. Bring a burning matchstick near the gas, if the
H2 is getting oxidised to H2O, CuO is getting reduced gas burns with ‘pop’ sound, the gas is H2.
to Cu.
It shows oxidation and reduction occur simultaneously. 87. Define the term decomposition reaction. Give
one example each of thermal decomposition and
82. When magnesium ribbon bums in air or oxygen, a electrolytic decomposition reactions.
product is formed. State the type of chemical reaction Ans : [CBSE 2016]
and name the product formed in the reaction. Write
Decomposition reaction: The reaction in which a
balanced chemical equation for the reaction.
compound is broken down into simpler elements or
Ans : [CBSE 2009(C)] compounds:
Heat
It is a combination reaction. The product formed is a. CaCO3(s) CaO(s) + CO2(g)
magnesium oxide: b. 2H2O(l)
Electricity
2H2(g) + O2(g)
2Mg(s) + O2(g) $ 2MgO(s)
88. Name two salts that are used in black and white
83. Distinguish between a displacement reaction photography. Give equations for the reactions when
and a double displacement reaction. Identify the these are exposed to sunlight.
displacement and the double displacement reaction Ans : [CBSE 2016]
from the following reactions:
a. HCl(aq) + NaOH(aq) $ NaCl(aq) + H2O(l) AgBr (Silver bromide) and AgI (Silver iodide) are
b. Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s) used in black and white photography.
sunlight
Ans : [CBSE 2009] 2AgBr(s) 2Ag(s) + Br2(g)
sunlight
2AgI(s) 2Ag(s) + I2(g)
Displacement Reaction: When a more reactive metal
displaces a less reactive metal from its salt solution. 89. State one example each characterised by following
Double displacement reaction: When two compounds along with suitable chemical equation.
exchange their ions to form two new compounds. a. Change in state,
a. Double displacement reaction. b. Evolution of gas,
b. Displacement reaction. c. Change in temperature.
84. What is an oxidation reaction? Give an example of Ans : [CBSE 2016]
oxidation reaction. Is oxidation an exothermic or an a. Change in state:
endothermic reaction? AgNO3(aq) + HCl(aq) $ AgCl(s) + HNO3(aq)
Ans : [CBSE 2009] b. Evolution of gas:
 CaCO3 ^ s h + 2HCl ^dilh $ CaCl 2 ^aqh + H 2 O ^ l h + CO2 ^g h 95. In a schematic diagram for the preparation of hydrogen
c. Change in temperature: gas as shown in the figure. What would happen if the
d. CH4(g) + 2O2(g) $ CO2(g) + 2H2O(l) + Heat following changes are made

90. Name the type of reactions represented by the

following equations:
a. CaO + H2O $ Ca(OH)2
b. 3BaCl2 + Al2(SO4) $ 3BaSO4 + 2AlCl3
Heat
c. 2FeSO4 Fe2O3 + SO2 + SO3
Ans : [CBSE 2015]
a. Combination reaction,
b. Double displacement reaction,
c. Decomposition reaction.

91. Write the chemical equation of the reaction in which

the following changes take place with an example of a. In place of zinc granules, same amount of zinc
each. dust is taken in the test tube?
a. Change in colour, b. Instead of dilute sulphuric, dilute hydrochloric
b. Change in tem-perature, acid is taken?
c. Formation of precipitate. c. Sodium hydroxide is taken in place of dilute
Ans : [CBSE 2015] sulphuric acid and the flask is heated?
a. Change in colour: Ans : [CBSE 2014, 2010]
Zn (s) + FeSO 4 (aq) $ ZnSO 4 (aq) + Fe (s) a. Zinc dust will react faster, H2(g) will be liberated
Pale green (Colourless)
at a faster rate.
b. Change in Temperature:
b. Same volume of H2(g) will be formed.
2Mg + O2(g) $ 2MgO(s) + Heat
c. On heating Zn with NaOH, hydrogen gas will be
c. Formation of precipitate:
formed at a faster rate.
Pb (NO 3) 2 (aq) + 2HCl (dil) $ Pbcl 2 (s) + 2HNO 3 (aq)
White ppt
96. (a) Why is it necessary to balance a chemical
92. State the type of chemical reactions and chemical
equation?
equations that take place in the following:
(b) Write the balanced chemical equation for the
a. Magnesium wire is burnt in air.
following reactions:
b. Electric current is passed through water.
(i) Natural gas burns in air to form carbon
c. Ammonia and hydrogen chloride gases are mixed.
dioxide and water.
Ans : [CBSE 2015] (ii) During respiration, glucose combines with
a. 2Mg(s) + O2(g) $ 2MgO(s); oxygen and forms carbon dioxide and water
b. Oxidation reaction along with the release of energy.
c. 2H2O(l) $ 2H2(g) + O2(g); Ans : [CBSE 2013]
Decomposition reaction
a. Chemical equation must be balanced so as to
d. NH3(g) + HCl(g) $ NH4Cl(s);
follow the law of conservation of mass.
Combination reaction
b. (i) CH4(g) + 2O2(g) $ CO2(g) + 2H2O(l)
93. Write the balanced chemical equations for the (ii) C 6 H 12 O 6 (s) + 6O 2 (g) $ 6CO 2 (g) + 6H 2 O (l) + Heat
following chemical reactions:
97. (i) Solid calcium oxide was taken in a container and
a. Hydrogen + Chlorine $ Hydrogen Chloride
water was added slowly to it.
b. Lead + Copper Chloride $ Lead chloride +
(a) Write the observations.
Copper
(b) Write the chemical formula of the product
c. Zinc oxide + Carbon $ Zinc + Carbon
formed.
Monoxide
(ii) What happens when carbon dioxide is bubbled
Ans : [CBSE 2013] through lime water (a) in small amount (b) in
a. H2(g) + Cl2(g) $ 2HCl(g) excess?
b. Pb(s) + CuCl2(aq) $ PbCl2(s) + Cu(s) Ans : [CBSE 2013, 2012, 2010]
c. ZnO(s) + C(s) $ Zn(s) + CO(g)
(i) (a) The container becomes hot and hissing sound
94. Write chemical equations for the reactions taking is produced.
place when (b) Ca(OH)2 is the formula of the product formed.
a. Iron reacts with steam (ii) (a) Lime water turn milky when CO2(g) is passed
b. Magnesium reacts with dil. HCl through it:
c. Copper is heated in air Ca(OH)2(aq) + CO2(g) $ CaCO3(s) + H2O(l)
(b) If excess of CO2 is passed milkiness disappears:
Ans : [CBSE 2014]
CaCO3(s) + CO2(g) + H2O(s) $ Ca(HCO3)2(aq)
a. 3Fe(s) + 4H2O(g) $ Fe3O4(s) + 4H2(g)
b. Mg(s) + 2HCl(dil) $ MgCl2(aq) 98. Write the balanced chemical equation for the following
c. 2Cu(s) + O2(g) $ 2CuO(s)
 reaction and identify the type of reaction. CuO(s) + Zn(s)
heat
Cu(s) + ZnO(s)
Thermite reaction, iron (III) oxide reacts with Ans : [CBSE 2011]
aluminium and give molten iron and aluminium oxide.
a. In respiration, energy is released, therefore, it is
Ans : [CBSE 2012]
considered an exothermic reaction.
Fe2O3(s) + 2Al(s) $ Al2O3(s) + 2Fe(l) b. Oxidation involves addition of O2 or loss of
It is displacement as well as redox reaction. electrons. Reduction involves addition of H2 or
gain of electrons.
99. An aqueous solution of metal nitrate ‘P’ reacts with
c. Zn is getting oxidised, CuO is getting reduced.
sodium bromide solution to form yellow precipitate
‘Q’ which is used in photography. ‘Q’ on exposure 104. Write balanced chemical equations for the following
to sunlight undergoes decomposition to form metal reactions:
present along with a reddish brown gas. Identify ‘P’ a. Hydrogen sulphide gas burns in air to give water
and ‘Q’ write the balanced chemical equation for the and sulphur dioxide.
chemical reaction. List the two categories in which b. Barium chloride reacts with zinc sulphate to give
reaction can be placed. zinc chloride and barium sulphate.
Ans : [CBSE 2012] c. Natural gas bums in air to form carbon dioxide
‘P’ is silver nitrate (AgNO3) and water.
AgNO3(aq) + NaBr(ag) $ AgBr(s) + NaNO3(aq) Ans : [CBSE 2011]
(P) (Yellow ppt)
This reaction is categorised as double displacement as a. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g)
well as precipitation reaction. b. BaCl 2 (aq) + ZnSO 4 (aq) $ BaSO 4 (s) + ZnCl 2 (aq)
sunlight c. CH4(g) + 2O2 $ CO2(g) + 2H2O(l)
2AgBr(s) 2Ag(s) + Br2(g)
The above reaction is photochemical decomposition
reaction. FIVE MARKS QUESTIONS
100. A green coloured hydrated metallic salt on heating
loses water of crystallisation molecules and gives a gas 105. Write balanced chemical equation for the following
with suffocating smell. Identify the salt and write the statements:
chemical equation for the reaction. a. NaOH solution is heated with zinc granules.
Ans : [CBSE 2011] b. Excess of carbon dioxide is passed through lime
water.
The salt is FeSO 4 $ 7H 2 O (Hydrated ferrous sulphate)
Heat c. Dilute sulphuric acid is added to sodium carbonate.
FeSO 4 $ 7H 2 O FeSO 4 (s) + 7H 2 O (l)
Heat d. Egg shell is dropped in hydrochloric acid,
2FeSO 4 (s) Fe 2 O 3 (s) + SO 2 (g) + SO 3 (g) e. Copper (II) oxide reacts with dilute hydrochloric
acid.
101. a.Can combination reaction be an oxidation
reaction? Ans : [CBSE 2016]
b. How will you test whether the gas evolved in a a. Zn(s) + 2NaOH $ Na2ZnO2 + H2
reaction is hydrogen? b. Ca(OH)2 + 2CO2 $ Ca(HCO3)2
c. Why does copper not evolve hydrogen on reacting c. Na2CO3 + H2SO4 $ Na2SO4 + H2O + CO2
with dilute sulphuric acid? d. CaCO3(s) + 2HCl(dil) $ CaCl2 + H2O + CO2
Ans : [CBSE 2011] e. CuO(s) + 2HC1 $ CuCl2 + H2O
a. Yes, combination reaction can be called a 106. Identify the type of chemical reaction in the following
oxidation reaction. statement and define each of them:
b. Bring a burning splinter near the gas, if it burns a. Digestion of food in our body.
with pop sound, it is hydrogen gas. b. Rusting of iron.
c. It is because copper is less reactive than hydrogen. c. Heating of manganese dioxide with aluminium
powder.
102. Write balanced equations for the following reactions:
d. Blue colour of copper sulphate solution disappears
a. Aluminium + Bromine $ Aluminium bromide
Heat when iron filings are added to it.
b. Calcium carbonate
e. Dilute hydrochloric acid is added to sodium
Calcium oxide + Carbon dioxide hydroxide solution to form sodium chloride and
sunlight
c. Silver chloride Silver + Chlorine water.
Ans : [CBSE 2011] Ans : [CBSE 2016]
a. 2Al(s) + 3Br2(g) $ 2AlBr3(s) a. Decomposition reaction: It is a process in which a
Heat
b. CaCO3(s) CaO(s) + CO2(g) compound is broken down into simple substances.
c. 2AgCl(s)
sunlight
2Ag(s) + Cl2(g) b. Oxidation: The process in which oxygen is added
or electrons are lost.
103. a.Why is respiration considered an exothermic c. Displacement reaction: The reaction in which a
reaction? more reactive element can displace a less reactive
b. Define the terms oxidation and reduction, element from its salt solution. Oxidation and
c. Identify the substance that is oxidised and reduced Reduction are taking place simultaneously in
in the following reaction: rusting of iron.
 d. Displacement reaction: The reaction in which a surface of copper powder turns black.
more reactive element can displace a less reactive c. On heating green coloured ferrous sulphate
element. crystals, raddish brown solid is left and smell
e. Neutralisation reaction: The reaction in which of a gas having odour of burning sulphur is
acid reacts with base to form salt and water. experienced.
d. Iron nails when left dipped in blue copper sulphate
107. Define chemical reaction. State four observations solution become reddish brown in colour and the
which helps to determine whether a chemical reaction blue colour of copper sulphate fades away.
has taken place or not. Write one example of each e. Quick lime reacts vigorously with water releasing
observation with a balanced chemical equation. a large amount of heat.
Ans : [CBSE 2015] Ans : [CBSE Sample Paper 2009]
Chemical reaction is a reaction which represents a a. Double displacement reaction,
chemical change. b. Oxidation,
a. Change in colour: c. Decomposition reaction,
Cu (s) + 2AgNO 3 (aq) $ Cu (NO 3) (aq) + 2Ag (s) d. Displacement reaction,
(Colourless) (Blue)
b. Evolution of gas: e. Combination reaction.
Heat
CaCO 3 (s) CaO (s) + CO (g)
(Carbon dioxide gas
c. Formation of precipitate:
Pb (NO 3) 2 (aq) + 2KI $ PbI 2 (s) KNO 3 (aq)
(Yellow ppt)
d. Change in temperature:
CaO(s) + H2O(l) $ Ca(OH)2 + Heat

108. a.Define a balanced chemical equation. Why should

an equation be balanced?
b. Write a balanced chemical equation for the
following reactions:
(i) Phosphorus burns in the presence of chlorine
to form phosphorus pentachloride.
(ii) Burning of natural gas.
(iii) The process of respiration.
Ans : [CBSE 2015]
a. Balanced chemical equation is a equation in which
number of atoms of various elements are equal on
both sides of the equation.
The equation should be balanced due to law of
conservation of mass.
b. (i) 2P(s) + 5Cl2(g) $ 2PCl5(S)
(ii) CH4(g) + O2(g) $ CO2(g) + 2H2O(l)
(iii) C6H12O6(s) + 6O2(g) $ 6CO2(g) + 6H2O(l)

109. (a) Write one example for each of decomposition

reaction carried out with the help of (i) Electricity,
(ii) Heat, (iii) Light.
(b) Which of the following statement is correct and
why?
Copper can displace silver from silver nitrate
solution and silver can displace copper from
copper sulphate solution.
Ans : [CBSE 2014]
Heat
a. (i) CaCO3(s) CaO(s) + CO2(g)
sunlight
(ii) 2AgBr(s) 2Ag(s) + Br2(g)
Electricity
(iii) 2H2O(l) 2H2(g) + O2(g)
b. Copper can displace Ag from AgNO3(aq) solution
because Cu is more reactive than Ag.
Cu (s) + 2AgNO 3 (aq) $ Cu (NO 3) 2 (aq) + 2Ag (s)

110. Identify the type of reactions taking place in each of

the following:
a. Barium chloride solution is mixed with copper
sulphate solution and white precipitate is formed.
b. On heating copper powder in china dish, the
Chap 7 : Control and Coordination www.cbse.online

CHAPTER 7
Control and Coordination

ONE MARK QUESTIONS of pollen tubes towards ovules?

Ans : [CBSE 2014]
Chemotropism.
1. Name two specialised tissues that provide control and
coordination in multicellular organisms. 10. Why endocrine glands release their secretions into the
Ans : [CBSE 2016] blood?
Nervous and muscular tissues. Ans : [CBSE 2014]
It is because endocrine glands are ductless.
2. List two body functions that will be affected if
cerebellum gets damaged. 11. At the time of puberty, both boys and girls show
Ans : [CBSE 2016] lots of changes in appearance. Name the hormones
responsible for these changes.
a. Walking in a straight line.
b. Picking up a thing from the ground. Ans : [CBSE 2014]
Testosterone in male and oestrogen in females.
3. Write the role of motor areas in brain.
Ans : [CBSE 2015]
Motor areas of the brain control the movement of
voluntary muscles.

4. Give the scientific names of the following regions of

the human brain:
a. Region for sight.
b. Region which controls salivation.
Ans : [CBSE 2015]
a. Temporal lobe (of the forebrain)
b. Medulla (of the hindbrain)

5. All information for our environment is detected by

specialised tips of some nerve cells. Write the name
given to such tips and also mention where are they 12. Which system facilitates the communication between
located? central nervous system and other parts of the body?
Ans : [CBSE 2014] Ans : [CBSE 2013]
Receptors. They are located in sense organs. Endocrine system.

6. State the function of: 13. Which gland secretes growth hormone in human
a. gustatory receptors beings?
b. olfactory receptors Ans : [CBSE 2013]
Ans : [CBSE 2014] Pituitary gland.
a. To detect taste.
14. Which mechanism control timing and amount of
b. To detect smell.
hormone released?
7. Which part of the nervous system controls reflex arcs? Ans : [CBSE 2013]
Ans : [CBSE 2014] Feedback mechanism.
Spinal cord.
15. Define‘Chemotropism’.
8. What type of movement is shown by mimosa plant Ans : [CBSE 2013]
leaves when touched with a finger? Chemotropism is a nastic response towards the
Ans : [CBSE 20141 chemicals like the germination of pollen tube when
Nastic movement. pollen grain lands on stigma.

9. Which tropic movement is responsible for the growth

16. What are hormones? through which information travels as an electrical
Ans : [CBSE 2013] impulse.
Dendrite $ a $ b$ End point of Neuron
Hormones are the chemical substances secreted in
trace amounts by specialised tissue called endocrine Ans : [Al 2018, CBSE 2017]
glands. (a) Tongue / Nose.
(b) a $ Cell body, b $ axon
17. Name two tissues that provide control and coordination
in multicellular animals. 27. Define neuron. Name the parts of the neuron where:
Ans : [CBSE 2013] a. information is acquired.
b. impulse must be converted into a chemical signal
(i) Nervous tissue (ii) Endocrine tissue.
for onward transmission?
18. What is synapse? Ans : [CBSE 2016]
Ans : [CBSE 2013] Neuron is a functional and structural unit of nervous
Synapse is the functional junction between two system. These cells are specialised for conducting
neurons. It is a gap junction point between nerve information via electrical impulses from one part of
endings of one neuron and dendrites of another neuron. the body to another.
(a) dendrites (b) end of axon.
19. Define ‘reflex action’.
Ans : [CBSE 2013]
Reflex action is a sudden, involuntary, spontaneous
response to the stimulus that is usually helpful to
protect ourselves from any kind of harm.

20. Name the sensory receptors found in the nose and on

the tongue.
Ans : [CBSE 2012]
Olfactory receptors, gustatory receptors.

21. Give one example of chemotropism.

Ans : [CBSE 2012]
The growth of pollen tube towards ovule.
28. Write two differences between the response of the
22. Name the plant hormone responsible for the promotion plants and response of the animals to stimuli?
of cell division. Ans : [CBSE 2015]
Ans : [CBSE 2010]
Cytokinin. Plants Animals
1. No specific or Specialised
23. How is nerve impulses get transmitted across the specialized tissue tissues are present
synapse? present for conduction in the body for
Ans : [CBSE S.R 2014-15] of information. conduction of
Neuron ending transmit the nerve impulse to dendrite of information.
next neuron through the chemical (neurotransmitter). 2. Plant cells change Specialised proteins
shape by changing the are found in muscle
24. What will happen to a plant shoot if sunlight falls
amount of water in cells which help in
on it from one direction only? What do you call this them. changing the shape.
movement?
Ans : [CBSE S.R 2012-13] 29. Trace the sequences of events through a reflex arc
Shoot will bend towards light. Phototropism. which occur when a bright light is focused on your
eyes.
25. How is spinal cord protected? Ans : [CBSE 2014]
Ans : [CBSE S.R 2010-11]
Vertebral column made by vertebrae protects the
spinal cord.

TWO MARKS QUESTIONS

26. (a) Name one gustatory receptor and one olfactory

receptor present in human beings.
(b) Write a and b in the given flow chart of neuron
30. How does feedback mechanism regulate the hormone
 secretion? Adrenaline. It increase the heart rate, breathing rate
Ans : [CBSE 2014] so that more blood can be pumped and oxygen can be
supplied to the muscles. Blood supply is cut off from
The feedback mechanism regulates the timing and
skin and sent to muscles. The action of this hormone
amount of hormone to be secreted, e.g., if a person
prepares the person to face the situation so that either
has more sugar in his blood, this is detected by the
he/she may run away or fight.
cells of the pancreas. As a result, more insulin will be
secreted to oxidise the sugar. In a reverse situation, 37. How does chemical coordination occur in plants?
the secretion of insulin will be reduced. Explain with the help of three examples.
31. What is meant by hydrotropism? Give an example. Ans : [CBSE 2014]
Ans : [CBSE 2013] In plants, chemical coordination occurs through
various phytohormones.
The response of a plant towards water is called
a. Auxins secreted by growing tissues. They provide
hydrotropism. The roots of plants show positive
growth of plants.
hydrotropism.
b. Gibberelins cause stem elongation, seed
32. Define phototropism and give one example. germination and flowering.
c. Cytokinins present in areas of actively dividing
Ans : [CBSE 2013]
cells like fruits, seeds. Promote cell division.
Movement of plant parts towards the light is called d. Abscisic acid inhibits growth and respond to
phototropism, e.g., stem of plant usually move towards environmental stress.
light.

33. Tendrils encircle or coil around the object in contact

with it. Elaborate.
Ans : [CBSE 2011, 2012, 2013]
Tendrils are sensitive to touch. When they come in
contact with any support, the part of the tendril in
contact with the object does not grow as rapidly as
the part of the tendril away from the object. This
causes the tendril to circle around the object and
thus, cling to it.

THREE MARKS QUESTIONS

38. Illustrate with the help of a diagram, the effect of

34. Name the hormones secreted by the following
endocrine glands and specify one function of each: auxins in different parts of a plant.
(a) Thyroid (b) Pituitary (c) Pancreas Ans : [CBSE 2014]
Ans : [All India 2018, CBSE 2017]
a. Thyroid: Secretes Throxine. It regulates
metabolism of carbo¬hydrates, fats and proteins.
b. Pituitary: Secretes growth harmone. Growth
harmone regulates growth and development of
body.
c. Pancreas: Secretes insulin. Insulin lowers blood
sugar level.

35. State how concentration of auxins stimulates the cells

to grow longer on the side of shoot which is away from
light?
Ans : [CBSE S.R 2016-17]
Auxin form in the shoot tip but diffuse toward the
part which is in shade/away from the light. 39. a. An old man is advised by his doctor to take less
sugar in his diet. Name the disease from which
The concentration on shady part increase
the man is suffering. Mention the hormone due
stimulation cells in this part to elongate. The side of
to imbalance of which he is suffering from this
shoot on this side grows longer than the part in light
disease. Which endocrine gland secretes this
hence bend towards light.
hormone?
36. Name the hormone which is secreted by the adrenal b. Name the endocrine gland which secretes growth
gland. How does this hormone help to deal with the hormone. What will be its effect on a person if
scary situations? there is:
Ans : [CBSE S.R 2016-17] (i) Deficiency of growth hormones?
 (ii) Excess secretion of growth hormones? 43. Give reasons:
Ans : [CBSE 2014] a. Pituitary is often termed as master endocrine
gland.
a. The man is suffering with the disease Diabetes.
b. Pancreas helps in digestion and also regulates
Insulin is the hormone which is responsible for
blood sugar level.
this disease. Pancreas secretes this hormone.
c. Adrenals are known as glands of emergency.
b. Pituitary gland.
(1) Deficiency of growth hormone causes Ans : [CBSE 2014]
dwarfism. a. Pituitary is often called as master endocrine gland
(2) Excess secretion of growth hormone cause because it controls and coordinates the secretion
gigantism in a person. of all the other endocrine glands.
b. Pancreas secretes pancreatic juice as well as a
40. a. Give the functions of cerebellum (any two). hormone called as insulin. Pancreatic juice helps
b. Name the components of central nervous system. in digestion whereas insulin regulates blood sugar
Ans : [CBSE 2014] level.
a. (i) Cerebellum is responsible for precision of c. Adrenalin is secreted directly into the blood and
voluntary action. is carried to different parts of the body. It acts on
(ii) It maintains the posture and balance of the heart. As a result, the heart beats faster in order
body. to supply more oxygen to our muscles. The blood
b. The components of central nervous system are: (i) to the digestive system and skin is reduced due
Brain (ii) Spinal cord. to contraction of muscles around small arteries
in these organs. This diverts the blood to our
41. a. Identify the phytohormone used by plants while skeletal muscles. The breathing rate also increases
performing the following functions: because of the contractions of the diaphragm
1. Cell division in shoot tip. and the rib muscles. All these responses together
2. Inhibiting growth on approach of unfavourable enable the animal body to get ready to deal with
conditions. the situation.
b. List in tabular form two differences between the
movement in ‘touch me not’ plant and movement 44. The two glands A and B which occur in pairs are
of shoot towards light. present in endocrine system. The pair of glands A is
found only in females whereas the pair of glands B
Ans : [CBSE 2014]
occur only in males. The gland A make and secrete
a. (1) Auxin, (2) Abscisic acid. hormone C whereas gland B make and secrete hormone
b. E. In addition to hormone, gland A makes gamete F
Movement of shoot Movement in “Touch whereas gland B makes gamete G.
towards light me not’ plant (Nastic a. What are glands A and B?
(Phototropism) movement) b. Name the hormone C and E
c. Name the gamete F and G.
1. It is slow response It is an immediate
Ans : [CBSE S.R 2013-14]
towards any stimulus. response towards a
stimulus. a. glands A - ovaries B-testes
b. Hormone C - oestrogen E-testosterone
2. It is directional. It is non-directional.
c. The gamete F - ova G-sperms
3. It is growth It is growth
dependent. independent. 45. ‘Brain and spinal cord are two vital organs of our
body’. How is our body designed to protect them?
42. Answer the following: Ans : [CBSE 2013]
a. Name the endocrine gland associated with brain.
Brain is protected a bony box contained in ‘ a fluid-
b. Which gland secretes digestive enzymes as well as
filled balloon which protects from shocks.
hormone?
c. Name the endocrine gland associated with Vertebral column protects the spinal cord or both
kidneys. are protected by protective layers called meninges,
d. Which endocrine gland is present in males but not protective fluid (CSF $ cerebrospinal fluid).
in females?
e. Which hormone is responsible for changes in 46. Draw and label a neuron. Explain how it carries
females during puberty? messages.
f. Iodine is necessary for the synthesis of which Ans : [CBSE S.P. 2012-13]
hormone? Information from the environment is detected by
Ans : [CBSE 2014] dendritic tip of a neuron located in the sense organ.
a. Pituitary gland, A chemical reaction sets off here and it creates an
b. Pancreas, electrical impulse which travels from dendrite to cell
c. Adrenal gland, body and then along the axon to its endings where it
d. Testes, sets off the release of some chemicals. The chemicals
e. Oestrogen, cross the synapse and set off a similar electrical
f. Thyroxine. impulse in dendrites of next neuron. Another synapse
 at the end of its axon delivers the impulse to the other Ans : [CBSE 2011]
cells like muscles cells / glands (effector organs) which a. Sensory neurons carry impulses from receptors to
react to perform the action. brain. Motor neurons carry impulses from brain
to effectors.
b. The brain is kept inside a bony box (skull). Inside
the box, the brain is contained in a fluid-filled
balloon which provides further shock absorption.
This fluid is known as Cerebrospinal Fluid (CSF).

47. Which hormone is secreted during emergency

situations like anger or excitement? How does it help
the human body to handle such situations?
or
How does our body respond when adrenaline is
secreted in to the blood?
Ans : [CBSE S.R 2012-13]
Adrenaline is secreted during emergency situations.
Heart beats faster, supply of more oxygen to muscles,
51. (a) What is reflex arc?
more blood to skeletal muscles, increased breathing
(b) What are the components of reflex arc?
rate. It provides energy to muscles to act swiftly.
(c) How do muscle cells move?
48. a. Name the part of brain which controls Ans : [CBSE 2011]
(1) voluntary action, a. The process of detecting the signal or the input
(2) involuntary action. and responding to it by an output action might be
b. What is the significance of the peripheral nervous completed quickly. Such a connection is commonly
system? Name the components of this nervous called reflex arc.
system and distinguish between the origin of the b. Stimulus " Receptors " Sensory neurons "
two. Spinal cord " Motor neurons " Effector.
Ans : [CBSE 2012] c. Muscle cells have special proteins that change
a. (1) Voluntary actions - cerebellum; their shape and arrangement in the cell in response
(2) Involuntary action — medulla oblongata. to electrical impulse. This leads the muscle cells
b. The communication between the central nervous shortening.
system and the other parts of the body is facilitated
52. a. If the cerebellum is not functioning properly, what
by the peripheral nervous system. Cranial nerves
are the activities of our body affected?
arise from the brain; spinal nerves arise from the
b. How do muscle cells move?
spinal cord.
Ans : [CBSE 2011]
49. a. Name the diseases by which a person is likely a. If the cerebellum is not functioning properly,
to suffer due to the deficiency of: (i) iodine (ii) voluntary action of our body will be affected
insulin maintaining the posture and balance of the body.
b. How the timing of secretion and amount of b. Muscle cells move by changing their shape so that
hormone secretion are regulated in human system. they get shorten.
Explain with example.
Ans : [CBSE 2012,13] 53. a. Name the hormone which is injected to a diabetic
patient.
a. (i) Goitre (ii) Diabetes.
b. Why should we use iodised salt in our diet?
b. The timing and amount of hormone released are
c. If iodine is insufficient in one’s diet, what might
regulated by feedback mechanisms, e.g., if the
be the deficiency disease and its symptoms?
sugar levels in blood rise, they are detected by the
cells of the pancreas which respond by producing Ans : [CBSE 2011]
more insulin. As the blood sugar level falls, insulin a. Insulin.
secretion is reduced. b. Iodine is necessary for the thyroid gland to
secrete thyroxine hormone. Thyroxine regulates
50. a. Differentiate between sensory neurons and motor carbohydrates, proteins and fat metabolism in the
neurons. body, to provide best balance for growth.
b. How is brain protected in our body? Name the c. If iodine is insufficient in one’s diet, iodine
part of the brain responsible for precision of deficiency disease called goitre occurs. Symptom
voluntary actions and maintaining body posture is swollen neck.
and balance of the body.
54. What are hormones? Name the hormone produced by
thyroid gland and state its function.
Ans : [CBSE S.R 2010-11]
Chemical coordination in animals occurs through
chemicals called hormones which are secreted by
endocrine glands. Thyroxin hormone.
It regulates metabolism of carbohydrates, fats
and proteins. It is advisable to consume iodized salt
in our food as iodine is required by our thyroid gland
to produce thyroxin hormone. If it lacks in our body
goiter may occur due to enlargement of thyroid in the
neck region.

55. Name the hormones secreted by thyroid, parathyroid Functions

and pancreas. a. Cerebellum which controls posture, balance of
Ans : [CBSE S.R 2010-11] body and accurate voluntary movements.
a. Thyroid gland: It secretes thyroxine hormone. b. Pons regulates respiration
b. Parathyroid gland: It secretes calcitonin hormone. c. Medulla oblongata which controls involuntary
c. Pancreas: It secretes two hormones: actions like blood pressure, salivation, vomiting
(a) Insulin (b) Glucagon etc.

56. Name the hormone synthesised at the shoot tips. How 58. Give the function(s) of the following plant hormones:
does it help the plant to respond to light? a. Auxins
b. Gibberellins
Ans : [CBSE 2010]
c. Cytokinins
Auxin is synthesised at the shoot tips when growing d. Abscisic acid
plant detects light and helps the cells to grow longer. e. Ethylene
When light is coming from one side of the plant, Ans : [CBSE 2015]
auxin diffuses towards the shady side of the shoot. a. Auxins promote cell elongation, root formation,
This concentration of auxin stimulates the cells to cell division, etc. It also promote fruit growth.
grow longer on the side of the shoot which is away b. Gibberellins stimulate stem elongation, seed
from light. Thus, the plant appears to bend towards germination and flowering.
light. c. Cytokinins help in breaking the dormancy of
seeds and buds. They delay ageing in leaves. They
also promote the opening of stomata.
d. Abscisic acid promotes falling of leaves and fruits.
e. Ethylene promotes ripening of fruits.

59. (a) Draw the structure of a neuron and label the

following on it:
Nucleus, Dendrite, Cell body and Axon.
(b) Name the part of neuron
(i) Where information is acquired.
(ii) Through which information travels as an
electrical impulse.
Ans : [CBSE 2013, Al 2008]
FIVE MARKS QUESTIONS a.

57. Draw a labelled diagram of human brain. Discuss

functions of cerebrum, cerebellum and medulla.
or
Draw and describe the role of various parts of human
brain.
Ans : [CBSE S.R 2016-17]
Human brain has three major parts:
a. Fore-Brain contains mainly cerebrum.
b. Mid-brain.
c. Hind-brain.
b. (i) Dendrite (ii) Axon.

60. Describe an activity to illustrate the phenomenon of

 phototropism and explain why does this occur.
Ans : [CBSE 2013]
a. Take a plant and make such an arrangement that
it receives the light coming from a window as
shown in the figure and observe it for few days.

b. Now, turn the flask so that the shoots are away

from light and the roots towards light. Leave it
undisturbed in this condition for a few days.
c. Again, observe carefully to find the difference in
the movement.
d. When growing plants detect light, auxin,
synthesized at the shoot tip, helps the cells to
grow longer. Auxin always diffuses towards the
shady side of the shoot. This concentrations of
auxin stimulates the cells to grow longer on the
side of the shoot which is away from light. Thus,
the plant appears to bend towards light.

61. (a) What is phototropism and geotropism? With

labelled diagrams describe an activity to show
that light and gravity change the direction that
plant part grows in.
(b) Mention the role of each of the following plant
hormones: (i) Auxin (ii) Abscisic acid.
Ans :
a. Phototropism It is tropic movements in the
direction of light or away from it e.g. shoots
bends towards light while roots grow away from
it. Hence shoot is positively phototropic and root
is negatively phototropic.

Geotropism: Growth of roots downward towards

the earth hence positively geotropic whereas
stem grows upward, away from earth, hence it is
negatively geographic.
b. Auxins: Synthesized at the shoot tip, helps the
cells to grow longer.
Abscisic acid: Inhibits growth, causes wilting and
falling of leaves.
Chap 4 : Carbon and Its Compounds www.cbse.online

CHAPTER 4
Carbon and Its Compounds

ONE MARK QUESTIONS (1) HCOOH Methanoic acid

(2) CH3COOH Ethanoic acid

8. Write the molecular formula of 2nd and 3rd member of

1. Write the molecular formula of first two members of
the homologous series whose first member is ethyne.
homologous series having functional group —Cl.
Ans : [CBSE 2017]
Ans : [CBSE 2017]
(1) HC / C—CH3 Propyne
(1) CH3Cl Chloromethane
(2) HC / C—CH2—CH3 1-Butyne
(2) CH3CH2Cl Chloroethane
9. Write the molecular formula of 2nd and 3rd member
2. Write the molecular formula of first two members of
of the homologous series whose first member is ethene.
homologous series having functional group —Br.
Ans : [CBSE 2017]
Ans : [CBSE 2017]
(1) CH2=CH—CH3 Propene
(1) CH3Br Bromomethane
(2) CH2=CH—CH2—CH3 1-Butene
(2) C2H5Br Bromoethane

3. Write the molecular formula of first two members of

homologous series having functional group —OH.
Ans : [CBSE 2017]
(1) CH3OH Methanol
(2) C2H5OH Ethanol

4. Write the molecular formula of 2nd and the 3rd

member of homologous series whose first member is
methane.
Ans : [CBSE 2017]
(1) CH3—CH3 Ethane
(2) CH3—CH2—CH3 Propane

5. Write the formula of first two members of homologous 10. Write the next homologue of each of the following:
series whose functional group is —CHO. a. C2H4
Ans : [CBSE 2017] b. C4H6
Ans : [CBSE 2016]
1. Methanal (1) C3H6, CH2=CH—CH3
(2) C5H8, HC=C—CH2—CH2—CH3

2. Ethanal 11. Name the following compounds:

a. CH3CH2OH
6. Write the formula of first two members of homologous
series whose functional group is .
Ans : [CBSE 2017] b.
Ans : [CBSE 2016]
a. Ethanol
1. 2-Propanone
b. Ethanal

12. Select the saturated hydrocarbons from the following:

2. 2-Butanone C3H6, C5H10, C4H10, C6H14, C2H4
7. Write the molecular formula of the first two members Ans : [CBSE 2016]
of the homologous series having functional group — C4H10, C6H14 are saturated hydrocarbons
COOH.
Ans : [CBSE 2017] 13. Write the name and structure of an alcohol with three
 carbon atoms in its molecules. 23. Write the next homologue of propanol CH3CH2CH2OH
Ans : [CBSE 2016] and butanal CH3CH2CH2CHO.
CH3CH2CH2OH, 1-Propanol Ans : [CBSE 2016,2011]
a. CH3CH2CH2CH2OH, Butanol
14. Write the name and structure of an alcohol with four b. CH3CH2CH2CH2CHO, Pentanal
carbon atoms in its molecule.
Ans : [CBSE 2016] 24. Unsaturated hydrocarbon gives a yellow flame with
lot of black smoke when burnt in oxygen. Give reason.
CH3CH2CH2CH2OH, 1-Butanol
Ans : [CBSE 2015]
15. Write the name and structure of an aldehyde with Unsaturated hydrocarbons have more amount of
four carbon atoms in its molecule. carbon, therefore burns with smoky flame due to
Ans : [CBSE 2016] incomplete combustion.

25. Write molecular formula of alcohol which can be

derived from butane.
Butanal Ans : .[CBSE 2015]
CH3CH2CH2CH2OH, 1-Butanol

16. Which element exhibits the property of catenation to 26. Carbon has four electrons in its valence shell. How
maximum extent and why? does carbon attain stable electronic configuration?
Ans : [CBSE 2016] Ans : [CBSE 2015]

Carbon because it can form strong covalent bond with Carbon can share four electrons to acquire stable
other carbon atoms due to smaller size. electronic configuration.

17. Write the name and formula of fourth member of 27. Write the name and formula of 2nd member of
alkane series. homologous series having general formula CnH2n.
Ans : [CBSE 2016] Ans : [CBSE 2015]

CH3—CH2—CH2—CH3, Butane CH2=CH—CH3 is second member of alkene.

18. What is a homologous series of carbon compounds? 28. Write the name and formula of 2nd member of
homologous series having general formulaC n H 2n + 2 .
Ans : [CBSE 2016]
Ans : [CBSE 2015]
Homologous series is series of organic compounds
which have same functional group and similar chemical CH3—CH3, Ethane
properties and each successive member has more — 29. Write the name and formula of 2nd member of
CH2 unit than the previous one. homologous series having general formula C n H 2n - 2 .
19. A colourless gas X has a formula C3H6. It decolourises Ans : [CBSE 2015]
bromine water. Write the chemical formula of ‘X’. HC / C—CH3, Propyne
Ans : [CBSE 2016]
30. Write the number of covalent bonds in the molecule
CH2=CH—CH3, Propene of propane, C3H6.
20. Draw the structural formula of methanoic acid. Ans : [CBSE 2015]
Ans : [CBSE 2016]
has 10 covalent bonds
Methanoic acid
31. Write the number of covalent bonds in the molecular
21. A molecule of ammonia has the formula NH3. Predict formula of butane, C4H10.
the total number of bonds present around nitrogen
Ans : [CBSE 2015]
atom.
Ans : [CBSE 2016]
has 13 covalent bonds
, it has three covalent bonds

32. Name the process by which unsaturated fats are

22. Write the number of covalent bonds in the molecule changed into saturated fats.
of ethane. Ans : [CBSE 2015]
Ans : [CBSE 2016,2015,2011 ] Hydrogenation

33. Write the name of each of the following functional

has 7 covalent bonds
 groups: compounds.
Ans : [CBSE 2014,2010]
a. —OH b. (a) Tetravalency (b) Catenation
Ans : [CBSE2015]
41. The molecular formula of A is C10H18 and B is C18H36.
a. Alcohol Name the homologous series to which they belong.
b. Ketone
Ans : [CBSE 2014]
34. Write the name and molecular formula of the first C10H18 belongs to alkyne, C18H36 belongs to alkene.
member of homologous series of alkynes.
Ans : [CBSE2015] 42. Write the names of next homologue of CH3CH2OH
and HCOOH.
HC=CH, Ethyne
Ans : [CBSE 2014]
35. Mention the functional group which always occurs at (i) CH3CH2CH2OH, Propanol
the terminal position of a carbon chain of an organic (ii) CH3COOH, Ethanoic acid
compound.
Ans : [CBSE 2015] 43. Will micelle formation take place when soap is
dissolved in organic solvent?
a. Aldehyde
b. Carboxylic acid Ans : [CBSE 2014]
No, micelles will not be formed in organic solvent.
36. The formula of citric acid is shown below:
44. Explain why washing clothes with hard water is not
effective.
Ans : [CBSE 2014]
Soap reacts with Ca 2+
and Mg 2+
ions present in hard
water to form scum.

45. Draw the structure of simplest ketone.

Ans : [CBSE 2014,2011]

State the name of —COOH functional group in citric

acid.
Ans : [CBSE 2014]
Carboxylic acid

37. Name the functional group in the following compounds:

a. CH3—CH2—CH2—COOH 46. Why do alkanes burn with blue flame?
b. CH3—CO—CH2—CH3
Ans : [CBSE 2013]
Ans : [CBSE 2014]
It is because they have less carbon and more hydrogen,
a. Carboxylic acid therefore, undergo complete combustion and produce
b. Ketone blue flame.
38. State the valency of each carbon atom in (i) an alkane 47. What happens when a small piece of sodium is
and (ii) an alkyne. dropped into ethanol?
Ans : [CBSE 2014] Ans : [CBSE 2013,2011]
i. The valency of ‘C’ in alkane is 4. Sodium ethoxide and H2 gas is formed
ii. The valency of ‘C’ in alkyne is also 4. 2C2H5OH + 2Na $ 2C2H5ONa + H2
39. Write the molecular formula of benzene and state the 48. What will you observe on adding a 5% alkaline KMnO4
number of double bonds in its structure. solution drop by drop to some warm ethanol taken in
Ans : [CBSE 2014] a test tube? Write the name of the compound formed
during the above chemical reaction.
Ans : [CBSE 2013,2011]
The purple colour of KMnO4 decolourises and ethanoic
is benzene or acid will be formed
Alk. KMNO
C2H5OH CH2OOH
4

ethanol ethanoic acid

These are 3 double bonds. 49. How is scum formed?

Ans : [CBSE 2012]
40. List two characteristic features of carbon which
when put together given rise to a number of carbon Ca 2+
and Mg
2+
ions react with soap (sodium stearate)
 to form calcium and magnesium stearate which is compounds.
insoluble in water and called scum.
59. Write the electron dot structure of ethene molecule
50. Name the functional group present in each of the (C2H4).
following organic compounds: Ans : [CBSE 2011]
a. C2H5—Cl
b. C2H5OH
Ans : [CBSE 2012]
a. Halogen
b. Alcohol
60. Write the electron dot structure of ethane molecule
51. Name the functional group present in each of the C2H6.
following compounds: Ans : [CBSE 2011]
a. HCOOH
b. C2H5CHO
Ans : [CBSE 2012]
a. Carboxylic acid
b. Aldehyde

52. Name the functional group present in each of the

61. Draw the structure of butanone molecule,
following compounds:
CH3COC2H5.
a. CH3COCH3
b. C2H5COOH Ans : [CBSE 2011]
Ans : [CBSE 2012]
a. Ketone
b. Carboxylic acid

53. Write the name and formula of the second member

of carbon compounds having functional group —OH. 62. Draw the structure of ethanoic acid molecule,
Ans : [CBSE 2012] CH3COOH.
CH3CH2OH, Ethanol Ans : [CBSE2011]

54. Write the name and formula of the first member of

series of carbon compound having functional group
—CHO.
Ans : [CBSE 2012]

63. Draw the structure of the hexanal molecule

Methanal
C5HnCHO.
55. Write the name and formula of the first member of Ans : [CBSE2011]
carbon compounds having functional group —COOH.
Ans : [CBSE 2012]

Methanoic acid

56. Write the name and formula of the 2nd member of the
series of carbon compounds whose general formula is 64. Butanone has four carbon per molecule of a compound.
CnH2n+1—OH. Name the functional group present in it.
Ans : [CBSE 2012] Ans : [CBSE 2011]

C2H5OH, Ethanol Ketone

57. Write the name and formula of 2nd member of the 65. Name the following compound:
series of carbon compounds whose general formula is
CnH2n.
Ans : [CBSE 2012]
CH2=CH—CH3, Propene
Ans : [CBSE 2011]
58. State the difference between oils and fats.
Ans : [CBSE Sample Paper 2012] 1-Hexyne

Oils are unsaturated whereas fats are saturated

66. Write the structural formula of chloroethane.
Ans : [CBSE 2010]

67. Name the carbon compound which on heating with

excess of cone. H2SO4 at 443 K gives ethene.
Ans : [CBSE 2009 (C)] Benzene has 3 double bonds whereas cyclohexane has
all single bonds.
Ethanol,
Conc. H 2 SO 4
CH3CH2OH CH2=CH2 + H2O 75. a. Write chemical name and formula of vinegar?
443 K
b. Describe with a chemical equation what happens
68. What is meant by saturated hydrocarbon? when sodium reacts with ethanol.
Ans : [CBSE 2009 (C)] Ans : [CBSE 2017,2012]
Those hydrocarbons in which valency of carbon is a. Vinegar contains ethanoic acid,
satisfied by single bonds only are called saturated
hydrocarbons.

69. Name the compound formed when ethanol is warmed b. Sodium ethoxide and hydrogen gas is formed.
with ethanoic acid in the presence of few drops of 2C2H5OH + 2Na $ 2C2H5ONa + H2
cone. H2SO4.
Ans : [CBSE 2009 (C)] 76. State reasons to explain why covalent compounds:
a. are bad conductors of electricity?
Ethyl ethanoate
Con. H 2 SO 4 b. have low melting and boiling points?
CH3COOH + CH3CH2OH T
Ans : [CBSE 2016]
CH3COOC2H5 + H2O a. Covalent compounds do not form ions, hence they
70. What is the difference in the molecular formula of
are bad conductor of electricity.
any two consecutive members of homologous series of b. Covalent compounds have weak intermolecular
organic compounds? forces of attraction, therefore, have low melting
and boiling points.
Ans : [CBSE 2008 (C)]
The difference between successive members of 77. What is homologous series? Write the name and draw
homologous series is of —CH2 unit. the structure of the second member of alkene series.
Ans : [CBSE 2016]
TWO MARKS QUESTIONS a. The series of organic compounds having same
functional group and similar chemical properties
is called homologous series.
71. Draw the structural formulae of the possible isomers b.
for the compound with molecular formula C3H6O.
Ans : [CBSE Sample Paper 2017]

72. Explain why cannot we have isomers of first three 78. List two characteristics of covalent compounds.
members of alkane family. Ans : [CBSE 2015]
Ans : [CBSE Sample Paper 2017, CBSE 2015] (i) They have low melting and boiling point.
It is because branching is not possible with carbon (ii) They do not conduct electricity.
atoms, that is why, there are no isomers till propane.
79. Name an element, other than carbon, which exhibits
73. Write balanced equations for the burning of (a) property of catenation up to seven or eight atoms. Are
methane (b) ethane in air. these compounds stable?
Ans : [CBSE 2017] Ans : [CBSE 2015]
(a) CH4(g) + 2O2(g) $ CO2(g) + 2H2O(l) Si and Sulphur (S8).
(b) 2C2H6(g) + 7O2(g) $ 4CO2(g) + 6H2O(l) No, these compounds are not stable, rather they are
reactive.
74. Compare the structures of benzene and cyclohexane
by drawing them. 80. Select alkenes and alkynes from the following:
C2H4, C3H4, C2H2, C4H8
Ans : [CBSE 2017]
Ans : [CBSE 2015,2014]
 Alkenes C2H4, C4H3 Alkynes C3H4, C2H2 88. Give the electron dot structure of chloro-methane. Also
write the formula and the name of next homologue of
81. Why are detergents preferred over soaps for washing it.
clothes in hard water? Explain.
Ans : [CBSE 2015]
Ans : [CBSE 2015,2014]
Detergents work well even with hard water because
their calcium and magnesium salts are soluble in
water. They do not form scum.

82. What happens when ethyl alcohol and acetic acid

react with each other in presence of cone. H2SO4?
Ans : [CBSE 2015,2013,2011]
Pleasant fruity smelling compound ester is formed
cone. H2SO4.
Con. H SO
CH3COOH + C2H5OH
2 4

T
CH3COOC2H5 + H2O
89. The structural formula of an ester is

83. Name the functional groups of the following

compounds:
a. b.
Write the structural formula of the corresponding
alcohol and acid.
c. R—OH d. R—X
Ans : [CBSE 2015]
Ans : [CBSE 2013]
a. Carboxylic acid
b. Ester
c. Alcohol
d. Halogen

84. Why is hydrogenation? What is its industrial

application? 90. How do the melting and boiling points of the
Ans : [CBSE 2015,2014] hydrocarbons change with increase in molecular mass?
Hydrogenation is a process of adding hydrogen to Ans : [CBSE 2012]
unsaturated compounds in presence of catalyst like Melting and boiling point of the hydrocarbons
nickel to form saturated hydrocarbons. Industrially, increases with increase in molecular mass because
it is used to convert vegetable oils to vegetable ghee. surface area increases which results an increase in
vander Waal’s forces of attraction between molecules.
85. List four characteristics of homologous series.
Ans : [CBSE 2014] 91. Write a chemical test to distinguish between ethanol
and ethanoic acid. [CBSE 2012]
a. All members are derived from same general
or
formula.
How would you distinguish experimentally between
b. All members have same functional group.
ethanol and ethanoic acid with the help of sodium
c. Each successive member differ by —CH2 unit.
hydrogen carbonate? Write the chemical equation for
d. All members can be prepared by same methods
the reaction involved.
of preparation.
Ans : [CBSE 2012]
86. Carbon does not form ionic compounds, why? Add NaHCO3 to each of them separately. Ethanol will
Ans : [CBSE 2015,2013] not react. Ethanoic acid will give brisk effervescence
Carbon cannot lose four electrons because high energy due to CO2.
is needed to remove four electrons. It cannot gain 4 CH3COOH + NaHCO3 $
electrons because 6 protons cannot hold 10 electrons. CH3COONa + H2O + CO2
That is why carbon cannot form ionic compounds. C2H5OH + NaHCO3 $ No reaction

87. What are soaps? Why do they form scum with hard 92. Explain the action of soap in removing an oily spot
water? from a piece of cloth.
Ans : [CBSE 2013] Ans : [CBSE 2011]
Soaps are sodium or potassium salts of fatty acids e.g. Cleansing action of soap: Soap has ionic end which
sodium stearate. They react with Ca2+ and Mg2+ ions is hydrophilic, interacts with water while carbon
in hard water to form calcium and magnesium salt chain is hydrophobic interacts with oil, grease. The
of fatty acids which are insoluble in water and called soap molecules orient themselves in a cluster in which
scum. hydrophobic tails are inside the cluster and ionic ends
 face outside. called homologous series.
These cluster are called micelles. These attract oil C2H6O(C2H5OH) and CH4O(CH3OH) belong to same
which is washed away by water. homologous series.

93. Draw electron dot structures of (i) C2H4 (ii) C2H5OH. 98. With the help of a suitable example explain in brief the
process of hydrogenation mentioning the conditions of
Ans : [CBSE 2011]
the reaction and also state any one physical property
of substances changes due to hydrogenation.
Ans : [CBSE 2010]
i.

ii. Liquid oil changes to solid ghee

94. Give reasons for the following:

a. Unsaturated hydrocarbons show addition
THREE MARKS QUESTIONS
reactions but not saturated hydrocarbons.
b. Carbon forms only covalent bonds. 99. A compound X on heating with excess of cone. H2SO4
Ans : [CBSE 2011] at 443 K gives an unsaturated compound Y. X also
a. Unsaturated hydrocarbons have double or triple reacts with sodium metal to evolve a colourless gas
bonds to which a molecule can be added whereas Z. Identify X, Y and Z. Write the equations of the
saturated hydrocarbons have single bonds chemical reaction of formation of Y and also write the
addition reaction cannot take place. role of conc. sulphuric acid in the reaction.
b. It cannot lose four electrons because high energy Ans : [CBSE 2016]
is required. It cannot gain four electrons because X is CH3CH2OH, Ethanol Y is Ethene, Z is H2.
6 protons cannot hold 10 electrons. Thus it shares Conc $ H SO
C 2 H 5 OH CH 2 = CH 2 + H 2 O
2 4

four electrons to form covalent bonds and become X

443K Y

stable. 2CH 3 CH 2 OH + 2Na $ 2CH 3 CH 2 ONa + H 2

Ethanol Sodium ethoxide Z

95. Write the name and molecular formula of an organic

Cone. H2SO4 acts as dehydrating agent.
compound having its name suffixed with ‘—ol’ and
having two carbon atoms in the molecule. With the 100. a.Why are most carbon compounds poor conductors
help of a balanced chemical equation indicate what of electricity?
happens when it is heated with excess of cone. H2SO4. b. Write the name and structure of a saturated
Ans : [CBSE 2010] compound in which carbon atoms are arranged in
a ring. Give the number of single bonds present in
this compound.
Ans : [CBSE 2018]
a. It is because covalent compounds do not form
ions, therefore, do not conduct electricity.

96. Write the names and molecular formulae of two

organic compounds having functional group suffixed b.
as ‘—oic acid’. With the help of a balanced chemical
equation explain what happens when any one of them
reacts with sodium hydroxide.
Ans : [CBSE 2010]
HCOOH and CH3COOH It has 18 single bonds.
Methanoic acid Ethanoic acid
HCOOH + NaOH $ HCOONa + H2O 101. Draw the structural formula of all the possible isomers
It is an acid-base reaction where a salt i.e., sodium of the compound with the molecular formula C3H6O
methanoate and H2O is formed. and also give electron dot structures.
Ans : [CBSE Sample Paper 2018] [CBSE 2013]
97. What is homologous series? Which of the following
organic compounds belong to the same homologous
series?
C2H6, C2H6O, C2H6O2, CH4O
Ans : [CBSE 2010]
The series of organic compounds having same
functional group and similar chemical properties is
 106. Two carbon compounds ‘X’ and ‘Y’ have the molecular
formula C3H6 and C4H10 respectively. Which one of the
two is most likely to show addition reaction? Justify
your answer. Also give chemical equation to explain
the process of addition in this case.
Ans : [CBSE 2017]
C3H6 will undergo addition reaction because it has
double bond.
Ni
CH2=CH—CH3 + H2 Heat CH3—CH2—CH3
Propene Propane

107. Complete the following chemical reactions:

a. C2H5OH + O2 $
102. An aldehyde as well as ketone can be represented by Conc. H SO
b. C2H5OH
2 4

the same molecular formula say C3H6O. Write their 443 K

structures and name them. State the relationship c. CH3COOH + NaHCO3 $

between two in language of science. Ans : [CBSE 2017]
Ans : [CBSE Sample Paper 2017-2018, CBSE 2016] a. C2H5OH + 3O2 $ 2CO2 + 3H2O
Con. H SO
b. C2H5OH CH2=CH2 + H2O
2 4

443 K

c. CH3COOH + NaHCO3 $
CH3COONa + H2O + CO2

108. The molecular formula of two carbon compounds

are C4H3 and C3H8. Which one is most likely to show
addition reaction? Justify your answer. Also give the
These are functional isomers.
chemical equation to explain the process of addition
103. The carbon compounds X and Y have the molecular reaction in this case.
formula C4H3 and C5H12 respectively. Which one of Ans : [CBSE 2017]
these is most likely to show addition reaction? Justify C4H3 will undergo addition reaction. It is because it is
your answer. Also give chemical equations to explain unsaturated compound.
the process of addition reaction in this case.
Ans : [CBSE 2017]
C4H3 will undergo addition reaction. It is because it has
double bond while C5H12 is a saturated hydrocarbon
which cannot undergo addition reaction.
109. Write the structural formula of ethanol. What happens
when it is heated with excess of conc. H2SO4 at 443 K?
Write the chemical equation for the reaction stating
the role of cone. H2SO4 in this reaction.
Ans : [CBSE 2017]
104. Complete the following equations: CH3CH2OH, Ethanol
Con. H SO
C2H5OH CH2=CH2 + H2O
2 4
a. CH3COOC2H5 + NaOH $ 443 K
b. CH3COOH + NaOH $
Conc. H SO Concentrated H2SO4 is dehydrating agent.
c. C2H5OH + CH3COOH
2 4

Ans : [CBSE 2017] 110. Distinguish between esterification and saponification

reaction with the help of equations for each. State one
a. CH3COOC2H5 + NaOH $ CH3COONa +
use of each (i) esters and (ii) saponification process.
C2H5OH
b. CH3COOH + NaOH $ CH3COONa + H2O Ans : [CBSE 2017]
Con. H SO
c. C2H5OH + CH3COOH CH3COOC2H5 Esterification
2 4

Con. H 2 SO 4
+ H2O C2H5OH + CH3COOH
CH3COOC2H5 + H2O
105. Complete the following reactions: Ester

a. CH3COOH + N2CO3 $ Saponification

b. CH4 + O2 $ CH3COOC2H5 + NaOH $
c. C2H5OH + Na $ CH3COONa + C2H5OH
Ans : [CBSE 2017] Esters are used in synthetic flavours, perfumes, etc.
Saponification process is used for manufacture of
a. 2CH3COOH + Na2CO3 $ 2CH3COONa + H2O
soaps.
+ CO2
b. CH4 + 2O2 $ CO2 + 2H2O 111. What happens when:
c. 2C2H5OH + 2Na $ 2C2H5ONa + H2 (Write chemical equation in each case)
 a. Ethanol is burnt in air? 114. Explain giving reasons, why carbon can neither form
b. Ethanol is heated with excess cone. H2SO4 at 443 C4+ cation nor C4- anion but forms covalent compounds
K? which are bad conductors of electricity and have low
c. A piece of sodium is dropped in ethanol. melting and boiling points.
Ans : [CBSE 2017] Ans : [CBSE 2017]
a. CO2 and H2O are formed. Carbon cannot lose four electrons because high energy
C2H5—OH + 3O2 $ 2CO2 + 3H2O is needed to remove four electrons. It cannot gain 4
b. Ethene is formed electrons because 6 protons cannot hold 10 electrons.
Con. H SO
CH3CH2OH CH2=CH2 + H2O
2 4

443 K It can share 4 electrons to form covalent bonds.

c. Hydrogen gas evolves out Covalent compounds do not conduct electricity
2CH3CH2OH + 2Na $ 2CH3CH2ONa + H2 because these do not form ions. They have low melting
and boiling points due to weak force of attraction
112. Explain esterification reaction with the help of a between molecules.
chemical equation. Describe an activity to show
esterification. 115. Write the molecular formula of benzene and draw
its structure. List in tabular form how covalent
Ans : [CBSE 2017]
compounds differ from ionic compounds.
Esterification is the process in which carboxylic Ans : [CBSE 2017]
acid reacts with alcohol in presence of conc. H2SO4 to
form pleasant fruity smelling compound ester.
ConcH SO
C2H5OH + CH3COOH
2 4

CH3COOC2H5 + H2O
Activity:
To carry out esterification reaction.
• Take 2 mL of ethanol (100% alcohol) in a test
tube.
• Add 2 mL of glacial acetic acid.
• Add few drops of conc. H2SO4.
• Set the apparatus as shown in diagram. Covalent compounds Ionic compounds
• Heat the mixture in test tube in water bath for 5
to 10 minutes observe what happens. 1. They are bad con- They are good conduc-
• Observation: Pleasant fruity smell is observed. ductor of electricity. tor of electricity.
• Conclusion: Ester is formed. 2. They have low They have high melting
melting and boiling and boiling points.
points.

116. What are hydrocarbons? Write the general formula

of (a) saturated hydrocarbons (b) unsaturated
hydrocarbons and draw the structure of one
hydrocarbon of each type.
Ans : [CBSE 2017]
Hydrocarbons are compounds of carbon and hydrogen
only
a. CnH2n+2 is general formula of saturated
hydrocarbon. For example, CH4

113. Name two oxidising agents that are used to convert

alcohols to acids. Distinguish between ethanol and b. CnH2n(alkenes) and CnH2n-2 (alkynes) are general
ethanoic acid on the basis of (a) litmus test (b) formulae of unsaturated hydrocarbons. For
reaction with NaHCO3. example,
Ans : [CBSE 2017]
These two oxidising agents will convert alcohols to
acids (i) Alkaline KMnO4 (ii) Acidified K2Cr2O7
a. Litmus test: Acetic acid turns blue litmus red but 117. What is an oxidising agent? What happens when
ethanol does not. oxidising agent is added to propanol? Explain with
b. NaHCO3 test: Acetic acid will give brisk the help of a chemical equation.
effervescence due to evolution of CO2 whereas Ans : [CBSE 2016]
ethanol will not react.
Oxidising agent is a substance which adds oxygen
or remove hydrogen. Propanol will get oxidised to
 propanoic acid. a.
Alkaline KMnO4
CH3CH2CH2OH + 2(O)
CH3CH2COOH+ H2O
b.
118. What are covalent compounds? Why are they different
from ionic compounds? List three characteristic
properties.
Ans : [CBSE 2016]
c.
Those compounds in which bonds are formed by
sharing of electrons are covalent compounds.
While ionic compounds are formed by complete
transfer of electrons.
122. Write three different chemical reactions showing the
Covalent compounds Ionic compounds conversion of ethanoic acid to sodium ethanoate.
Write balanced chemical equation in each case. Write
1. They have weak They have strong
the name of the reactants and products other than
intermolecular forces intermolecular forces of
ethanoic acid and sodium ethanoate in each case.
of attraction. attraction.
Ans : [CBSE 2016]
2. They have low They have high
melting and boiling melting and boiling a.
points. points.
3. They do not They conduct electrici- b.
conduct electricity. ty in molten state or in
aqueous solution.

119. When ethanol reacts with ethanoic acid in presence of c.

cone. H2SO4, a substance with fruity smell is produced.
Answer the following questions:
a. State the class of compounds to which fruity
smelling compounds belong. Write the chemical
equation and write the chemical name of the
product formed.
123. An organic compound ‘P’ is a constituent of wine.
b. State the role of cone. H2SO4 in this reaction.
‘P’ on reacting with acidified K2Cr2O7 forms another
Ans : [CBSE 2016] compound ‘Q’. When a piece of sodium is added to
a. The fruity smelling compounds are esters ‘Q’ a gas ‘R’ evolves which burns with a pop sound.
CH 3 COOH + C 2 H 5 OH
Con.H 2 SO 4
CH 3 COOC 2 H 5 + H 2 O Identify P, Q and R and write the chemical equations
Ethanoic acid Ethanol Ethyl Ethanoate Water of the reactions involved.
b. Cone. H2SO4 acts as dehydrating agent. Ans : [CBSE 2016]
120. Name the compound formed when ethanol is heated
with excess of cone. H2SO4 at 443 K. Also write the
chemical equation of the reaction stating the role of
cone. H2SO4 in it. What would happen if hydrogen is
added to the product in presence of catalyst such as Q is ethanoic acid,
Pd or Ni?
Ans : [CBSE 2016]

124. a. Define the term functional group. Identify the

functional group present in
Cone. H2SO4 acts as dehydrating agent.

b. What happens when 5% alkaline KMnO4 solution

121. Write the chemical equation of the reaction of ethanoic is added drop by drop to warm ethanol taken in
acid with the following: a test tube? State the role of alkaline KMnO4
a. Sodium solution in this reaction.
b. Sodium hydroxide, Ans : [CBSE 2016]
c. Ethanol.
Write the name of one main product of each reaction. a. Functional group is an atom or group of atoms
which determine chemical properties of organic
Ans : [CBSE 2016]
compounds. (a) Aldehyde, (b) Carboxylic acid.
 b. Ethanoic acid is formed.
5%alkaline
CH3 CH2 OH + 2 [O] KMnO 4
CH 3 COOH
KMnO4 acts as oxidising agent.

125. Under which condition an oxidation reaction can be

called as combustion reaction. Illustrate your answer Esterification is the process of forming ester
with example.
129. Write any three physical properties and three uses of
Ans : [CBSE 2016]
ethanol.
When oxidation reaction produces heat as well as Ans : [CBSE 2016]
light it is called combustion reaction.
CH4 + 2O2 $ CO2 + 2H2O + heat + light Properties
It is oxidation as well as combustion reaction. a. Ethanol has specific smell.
b. It is soluble in water.
126. a.Give chemical tests to detect the presence of (a) c. It has burning taste.
ethanol (b) ethanoic acid. Uses
b. Why ethanoic acid is called glacial acetic acid? a. It is used as solvent.
Ans : [CBSE 2016] b. It is used as an antiseptic.
c. It is used in wine, beer, whisky, etc.
(i) (a) Ethanol reacts with Na to liberate d. It is used for preparation of ethanoic acid, ethyl
H2 gas ethanoate (esters).
2CH 3 CH 2 OH + 2Na $ 2CH 3 CH 2 ONa + H 2
(b) Ethanoic acid gives brisk effervescence of CO2 130. Explain the following reactions with chemical
with NaHCO3 equations:
CH 3 COOH + NaHCO 3 $ a. Oxidation
CH 3 COONa + H 2 O + CO 2 b. Hydrogenation
(ii) It is because pure acetic acid (anhydrous) solidifies c. Substitution
into solid crystals just below the room temperature at Ans : [CBSE 2016]
16.7°C and look like glacier of snow.
a. Oxidation
127. a.Chemical properties of ethanol is different from
methyl ethanoate. Justify the statement with
proper reason.
b. Methyl ethanoate is used in making perfume.
Justify. b. Hydrogenation
c. Ethanol is converted into ethene when excess of
cone. H2SO4 is added. Justify with the help of
reaction. c. Substitution
Ans : [CBSE 2016]
a. Chemical properties of a compound depends on its
functional group. Ethanol and methyl ethanoate
131. C3H6, C4H8 and C5H10 belong to same 1 homologous
have different functional group thus behave
series.
differently. CH3CH2OH has functional group —
a. Define homologous series.
OH. It has specific smell, reacts with Na metal
b. Why the melting and boiling point of C5H10 is
to liberate H2. CH2COOCH3 has ester (RCOOR’)
higher than C4H3?
as functional group. It has pleasant fruity smell,
c. Arrange these hydrocarbons in order of increasing
undergoes saponification reaction with NaOH.
boiling points.
b. It is due to pleasant fruity smell.
c. Conc H2SO4 dehydrates ethanol to ethene. Ans : [CBSE 2016]
ConcH SO
CH 3 CH 2 OH CH 2 = CH 2 + H 2 O a. The series of organic compounds having same
2 4

443K
functional group and similar chemical properties
128. The structural formula of an ester is is called homologous series.
b. C5H10 has higher molecular mass, more surface
area, more van der Waal’s forces of attraction,
hence higher boiling point than C4H8.
c. C3H6 < C4H8 < C5H10
Write the structural formula of the acid and the
132. The general formula of three compounds A, B and C
alcohol from which it might be prepared. Name the
is C n (H 2n . ‘B’ has highest boiling point and ‘C’ has
process of formation of an ester.
lowest boiling point.
Ans : [CBSE 2016] a. Mention the type of compounds A, B, C.
b. Which of these have minimum number of carbon
atoms?
c. Name the homologous series to which A, B and
 C belong. this reaction is referred to as substitution reaction.
Ans : [CBSE 2016] Ans : [CBSE 2015]
a. A, B, C are unsaturated compounds.
b. C has minimum number of carbon atoms..
c. They belong to alkene homologous series.

133. Draw the electron dot structure of ethyne. A mixture

of ethyne and oxygen is burnt for welding. In your Sunlight
opinion, why cannot we use a mixture of ethyne and CH2Cl2 + Cl2 CHCl 3
+ HCl
Trichloromethane
air for this purpose? Sunlight
CHCl3 + Cl2 CCl + HCl
Ans : [CBSE 2015] 4
Tetrachloromethane

This reaction is called substitution reaction because

HC / CH, Ethyne, hydrogen atom is being substituted by ‘Cl’ in each
step.
Ethyne and oxygen will produce lot of heat on
combustion needed for welding whereas ethyne and 138. What is difference between the molecule of soaps and
air will not produce enough heat needed for welding detergents, chemically? Explain the cleansing action
purposes. of soaps.
Ans : [CBSE 2015]
134. Classify the following carbon compounds into two
homologous series and name them. Soaps are sodium or potassium salts of fatty acids.
C3H4, C3H6, C4H6, C4H8, C5H8, C5H10 They contain —COONa group. Detergents are sodium
or potassium salts of sulphonic acids. They contains
Ans : [CBSE 2015]
—SO3Na or —SO4Na group. Soap has ionic end which
The series of organic compounds having same is hydrophilic, interacts with water while carbon
functional group and similar chemical properties is chain is hydrophobic interacts with oil, grease. The
called homologous series. soap molecules orient themselves in a cluster in which
Alkene: C3H6, C4H8, C5H10 hydrophobic tails are inside the cluster and ionic ends
Alkyne: C3H4, C4H6, C5H3 face outside. These cluster are called micelles. These
attract oil which is washed away by water.
135. Write the name and general formula of a chain of
hydrocarbons in which an addition reaction with 139. What is meant by isomers? Draw the structures of two
hydrogen is possible. State the essential conditions for isomers of butane, C4H10. Explain why we cannot have
an addition reaction. Stating this condition, write a isomers of first three members of alkane series.
chemical equation giving the name of the reactant and Ans : [CBSE 2015]
the product of the reaction.
Isomers are those compounds which have same
Ans : [CBSE 2015]
molecular formula but different structural formula.
Alkenes C n H 2n Alkynes C n H 2n - 2 CH3– CH2– CH2– CH3
In above two series of hydrocarbons, addition of H2 Butane
is possible.
Hydrogen is added in presence of nickel as catalyst
and heating is needed.

140. Write the molecular formula of the following

136. Why should we prefer vegetable oils over animal fats compounds and draw their electron dot structures:
for cooking food? Give a balanced chemical equation (a) Ethane (b) Ethene (c) Ethyne
for reaction of hydrogenation of vegetable oils. Name Ans : [CBSE 2015]
the catalyst in the reaction.
Ans : [CBSE 2015]
Vegetable oils are unsaturated and do not lead to a. , , C2H6
formation of cholesterol. Animals fats are saturated
lead to formation of cholesterol which can be deposited
in arteries.

b. , , C2H4

c. , , C2H2
137. Convert CH4 into CC14 by substituting hydrogen
atom with chlorine atom in successive reactions. Why
141. Why is homologous series of carbon compounds so
 X
called? Write the chemical formula of two consecutive KMnO 4 /KOH
members of any two homologous series and state the CH3CH2OH + 2[O] CH3COOK
part of these compounds that determines their (a) H+
CH3COOH + K+
physical and (b) chemical properties.
X is CH3COOC2H5, ethyl ethanoate.
Ans : [CBSE 2015]
Homologous means members of same family that 145. What is meant by homologous series of carbon
is why series of carbon compounds having same compounds? Write the general formula of (i) alkenes,
functional group and similar properties is called and (ii) alkynes. Draw the structures of the first
homologous series. member of each series to show the bonding between
Homologous series of alcohol. the two carbon atoms.
CH3OH Methanol Ans : [CBSE 2014]
C2H5OH Ethanol The series of organic compounds having same
CH3— and C2H5— groups determine physical functional group and similar chemical properties is
properties and —OH group determines chemical called homologous series.
properties. Homologous series of aldehyde. i. Alkenes CnH2n
CH3OH Ethanol
C2H5OH Propanal
Here, CH3—and C2H5— groups determine physical
properties while —CHO group determines chemical
properties.
ii. Alkynes CnH2n–2
142. What are esters? How are they prepared? List two
uses of esters.
Ans : [CBSE 2014]
Esters are pleasant fruity smelling compounds with 146. Write the chemical equations to show what happens
general formula R—COOR’. They are prepared by when
reaction of carboxylic acid and alcohol in presence a. an ester reacts with a base?
of cone. H2SO4. b. methane is treated with chlorine in the presence
Conc. H SO
CH3COOH + C2H5OH
2 4

of sunlight?
CH3COOC2H5 + H2O c. ethanol reacts with ethanoic acid in the presence
Uses of sulphuric acid?
i. They are used in cold drinks and ice creams as Ans : [CBSE 2014]
synthetic flavours.
ii. They are used in perfumes. a. CH3COOC2H5 + NaOH
CH3COONa + C2H5OH
143. State the meaning of functional group in an organic Sunlight
b. CH4 + Cl2 CH3Cl + HCl
compound. Write the formula of the functional group
present in alcohols, aldehydes, ketones and carboxylic c. CH3COOH + C2H5OH
Conc. H 2 SO 4

acids. CH3COOC2H5 + H2O

Ans : [CBSE 2014]
147. Write the respective chemical equations to show what
Functional group is an atom or group of atoms which
determine chemical properties of organic compounds happens when
(a) Aldehyde, (b) Carboxylic acid. a. methane is burned in presence of oxygen?
b. ethanol is heated with concentrated sulphuric acid
at 443 K?
–OH Alcohol; Aldehyde c. ethanol reacts with ethanoic acid in the presence
of an acid acting as a catalyst?
Ans : [CBSE 2014]

Ketone; Carboxylic acid a. CH4 + 2O2 CO + 2H2O

2
Conc. H 2 SO 4
b. CH3CH2OH 443 K
CH2=CH2 + H2O
144. A carboxylic acid (molecular formula C2H4O2) reacts Conc. H 2 SO 4
with an alcohol in the presence of an acid catalyst to c. CH3COOH + C2H5OH
form a compound X. The alcohol on oxidation with CH3COOC2H5 + H2O
alkaline KMnO4 following by acidification gives the
148. Write chemical equations to describe two different
same carboxylic acid C2H4O2. Write the name and
oxidations of ethanol. List two uses of ethanol.
structure of (i) carboxylic acid, (ii) alcohol and (iii)
the compound ‘X’. Ans : [CBSE 2015]
K 2 Cr2 O 7 /H 2 SO 4
Ans : [CBSE 2014,2013] CH3CH2OH + 2[O] CH3COOH
Conc. H 2 SO 4
CH3COOH + C2H5OH CH2CH2OH + O2 CO2 + H2O + Heat + Light
Ethanoic acid Ethanol Ethanol is used as an antiseptic and solvent
CH3COOC2H5 + H2O
149. A carbon compound X turns blue litmus to red and
 has a molecular formula C2H4O2. Identify X and draw compounds. (1) Alcohol, (2) Carboxylic acid.
its structure. Write chemical equation for the reaction a. Soaps do not work well with hard water as form
and name of the product formed in each case when X insoluble scum whereas detergents work well with
reacts with hard water.
a. ethanol in the presence of concentrate H2SO4.
b. sodium carbonate. 153. Give reasons for the following observations:
a. The element carbon forms a very large number of
Ans : [CBSE 2013]
compounds.
X is CH3COOH b. Air holes of a gas burner have to be adjusted when
the heated vessels get blackened by the flame.
c. Use of synthetic detergents causes pollution of
water.
Ans : [CBSE 2009]

a. CH3CH2OH
Conc. H 2 SO 4
CH2=CH2 + H2O a. It is due to tetravalency of carbon and property of
443 K
catenation shown by carbon to maximum extent.
b. 2CH3COOH + Na2CO3 $ b. Air holes must be kept open fully so that complete
2CH3COONa + H2O + CO2 combustion of fuel takes place producing blue
flame.
150. What is meant by isomers? “We cannot have isomers c. Some of detergents are not bio¬degradable, they
of first three members of alkane series.” Give reason create water pollution.
to justify this statement. Draw the structures of two
isomers of pentane, C5H12. 154. a.Why are covalent compounds generally poor
Ans : [CBSE 2013] conductors of electricity?
b. Name the following compound:
Isomers are those compounds which have same
molecular formula but different structural formula.
CH3– CH2– CH2– CH2– CH3
Pentane

c. Name the gas evolved when ethanoic acid is

added to sodium carbonate. How will you test the
presence of this gas.
Ans : [CBSE 2008]
151. An ester has the molecular formula C4H8O2. Write its a. It is because they do not form ions in their
structural formula. What happens when this ester is aqueous solution.
heated in the presence of sodium hydroxide solution? b. Propanone
Write the balanced chemical equation for the reaction c. Carbon dioxide gas will be liberated. Test: Pass
and name the products. What is a saponification the gas through lime water. If lime water turns
reaction. milky it shows the presence of CO2 gas.
Ans : [CBSE 2010]
FIVE MARKS QUESTIONS
is structural formula.
155. You are given balls and stick model of six carbon
When ester is heated with NaOH, sodium salt of acid
atoms and fourteen hydrogen atoms and sufficient
and alcohol are formed. It is called saponification
number of sticks. In how many ways one can join the
reaction.
models of six carbon atoms and fourteen hydrogen
atoms to form different molecules of C6H14.
Ans : [CBSE Sample Paper 2017-2018]
There are five ways in which six carbons can be joined
with 14 hydrogen atoms.

i.
152. a.What is meant by a functional group in an organic
compound? Name the functional group present in
(1) CH3CH2OH
(2) CH3COOH
b. State one point of difference between soap and
synthetic detergent. ii.
Ans : [CBSE2009]
a. Functional group is an atom or group of atoms
which determine chemical properties of organic
 iii.

Alkene CnH2n

iv. Alkyne CnH2n–2 Ethyne

Hydrogenation i.e. addition of H2 leads to formation of
alkanes from alkenes.
Ni
CH2 = CH2 + H2 heat CH3 – CH3

158. Complete the following chemical equations and write

v.
the chemical name of the products formed.
a. CH2=CH2 + H2 $
b. CH3COOH + NaOH $
H SO
c. CH3CH2OH
2 4

Check Anser : d. HCOOH + Na $

Alk $ MnO
e. C2H5OH
4

156. Soaps and detergents are both types of salts. State

the difference between the two. Write the mechanism Ans : [CBSE 2018]
of the cleansing action of soaps. Why do soaps not
a. CH2= CH2 + H2 CH3– CH3
form lather (foam) with hard water? Mention any
two problems that arise due to the use of detergents Ethane

instead of soaps. b. CH3COOH + NaOH

Ans : [CBSE 2017] CH3COONa + H2O
Sodium ethanoate
a. Soaps are sodium or potassium salts of fatty c. CH3CH2OH
Conc. H 2 SO 4
CH2= CH2 + H2O
D
acids e.g. —COONa. Detergents are sodium or Ethene

potassium salts of sulphonic acids e.g. —SO3Na d. 2HCOOH + 2Na 2HCOONa + H2

or —SO4Na Alk. KMnO 4
Sodium methanoate

b. Soaps are sodium or potassium salts of fatty e. C2H5OH CH3COOH + H2O

acids. They contain —COONa group. Detergents Ethanoic acid
are sodium or potassium salts of sulphonic acids.
They contains —SO3Na or —SO4Na group. Soap 159. a.Give a chemical test to distinguish between
has ionic end which is hydrophilic, interacts with saturated and unsaturated hydrocarbons.
water while carbon chain is hydrophobic interacts b. Name the products formed when ethane burns in
with oil, grease. The soap molecules orient air. Write the balanced chemical equation for the
themselves in a cluster in which hydrophobic tails reactions showing two types of energies liberated.
are inside the cluster and ionic ends face outside. c. Why is reaction between methane and chlorine in
These cluster are called micelles. These attract oil presence of sunlight is considered a substitution
which is washed away by water. reaction.
c. Soaps react with Ca2+ and Mg2+ ions in hard water Ans : [CBSE 2016]
to form calcium or magnesium salts of fatty acids a. Saturated hydrocarbons will not react with
which are insoluble in water and thus interfere in bromine water whereas unsaturated hydrocarbons
action of soap, will decolourise it.
d. (i) Detergents are more expensive than soaps. b. Carbon dioxide and water will be formed.
(ii) Some detergents are not biodegradable i.e. 2C2H6 + 7O2 $ 4CO2(g) + 6H2O(l)
will create pollution. + Heat + Light
157. Why are certain compounds called hydrocarbons? c. It is because hydrogen atom is substituted by
Write the general formula for homologous series of halogen atom, that is why it is called substitution
alkanes, alkenes and alkynes and also draw the reaction.
structure of the first member of each series. Write 160. a.You have three unlabelled test tubes containing
the name of the reaction which converts alkene into ethanol, ethanoic acid and soap solution. Explain
alkane. Also write the chemical equation to show the the method you would use to identify the
necessary conditions for the reaction to occur. compounds in different test tubes by chemical
Ans : [CBSE 2017] tests using litmus paper and sodium metal.
Compounds of carbon and hydrogen are called b. Give reason of formation of scum when soaps are
hydrocarbons. used with hard water.
Alkane CnH2n+2 Ans : [CBSE 2016]
 a. Red litmus paper will become blue in soap solution the concerned chemical reaction.
only. Ethanoic acid will turn blue litmus red only. (1) Ethanol to ethene
Ethanol will react with Na metal to form sodium (2) Ethanol to ethanoic acid
ethoxide and hydrogen gas will be liberated. b. Give one example with chemical equation for the
b. Soaps are sodium or potassium salts of fatty acids following reactions:
which react with Ca2+ and Mg2+ ions in hard water (1) Substitution reaction
to form calcium or magnesium salts of fatty acids (2) Saponification reaction
which are insoluble in water called scum. (3) Combustion reaction
Ans : [CBSE 2014]
161. What are micelles? Why does it form when soap is
Conc. H 2 SO 4
added to water? Will a micelle be formed in other a. (1) CH3CH2OH D
CH2= CH2 + H2O
solvents such as ethanol also? State briefly how the Ethanol Ethene

formation of micelles help to clean the clothes having (2) CH3CH2OH

K 2 Cr2 O 7 /Conc. H 2 SO 4

oily spots. CH3COOH + H2O

Ans : [CBSE 2016] b. (1) Substitution reaction
Micelles are cluster of molecules in which hydrophobic CH4 + Cl2
Sunlight
CH3Cl + HCl
tails are inside the cluster 3 and the ionic ends are at
the surface of clusters. Soap molecules when dissolved (2) Saponification reaction
in water they form a cluster due to hydrophobic part
CH3COOCH3 + NaOH
of molecules orient themselves away from water.
CH3COONa + CH3OH
So they arrange towards inside of the cluster while
hydrophilic part remain outside of cluster. (3) Combustion reaction
No, micelles will not be formed in alcohol. Soap in
CH4 + 2O2 CO2 + 2H2O
form of micelles is able to clean because the oily dirt
will be collected in centre of micelle which is rinsed 165. Identify the compounds ‘A’ to ‘E’ in the following
away by water. sequence:
KMNO 4 /KOH
162. a.Differentiate between soap and detergent. a. CH3CH2OH dil. HCl
A + H2O
b. Explain why, soaps form scum with water whereas b. CH3CH2OH + A B + H2O
Conc. H 2 SO 4
D
detergent do not.
c. B + NaOH C + CH3CH2OH
Ans : [CBSE 2015]
d. A + NaHCO3 C + D + H2O
e. CH3CH2OH + E CH3CH2ONa + H2
Soap Detergent
Ans : [CBSE 2013]
1. Sodium salts of fatty Sodium salts of KMNO 4 /KOH
acids. sulphonic acids. a. CH3CH2OH dil. HCl
CH3COOH + H2O
‘A’
2. They do not work They work well even
Conc. H 2 SO 4
well with hard water. with hard water. b. CH3CH2OH + CH3COOH D
‘A’
b. Sodium salts of fatty acids (soaps) react with CH3COOCH2CH3 + H2O
Ca2+ and Mg2+ ions in hard water to form insoluble ‘B’

salts called scum. Detergents form soluble salts c. CH3COOCH2CH3 + NaOH

‘B’
with Ca2+ and Mg2+.
CH3COONa + CH3CH2OH
‘C’
163. a.How is vinegar made?
d. CH3COOH + NaHCO3
b. What is glacial acetic acid? What is its melting
CH3COONa + CO2 + H2O
point? ‘C’ ‘D’
c. Why are carboxylic acids called weak acids? e. 2CH3CH2OH + 2Na 2CH3CH2ONa + H2
d. Write the name and formula of compounds ‘E’

formed when the ester CH3COOC2H5 undergoes A is CH3COOH, ‘B’ is CH3COOCH2CH3, *C’ is
saponification. CH3COONa, ‘D’ is CO2, ‘E’ is Na (Sodium metal).
Ans : [CBSE 2014, 2013]
166. An organic compound “X’ on heating with cone.
a. Vinegar is 5-8% solution of acetic acid (Ethanoic H2SO4 forms a compound ‘Y’ which on addition of
acid) in water. It can be made by fermentation of one molecule of hydrogen in the presence of nickel
ethanol in presence of oxygen. forms a compound ‘Z’. One molecule of compound
b. Glacial acetic is pure (100%) acetic acid. Its ‘Z’ on combustion forms two molecules of CO2 and
melting point is 290 K. three molecules of H2O. Identify giving reasons the
c. They do not ionise completely in aqueous solution. compounds X’, ‘Y’ and ‘Z’. Write the chemical
d. CH3COOC2H5 + NaOH equations for all the chemical reactions involved.
CH3COONa + C2H5OH Ans : [CBSE 2013]
Sodium ethanoate Ethanol Conc. H 2 SO 4
CH3CH2OH heat
CH2 = CH2 + H2O
‘X’ ‘Y’
164. a. How will you bring out following reactions? Write Ni
CH2 = CH2 + H2 CH3 – CH3
‘Y’ ‘Z’
 C2H6 + (7/2)O2 2CO2 + 3H2O Ethanol Ethanoic acid
‘Z’ on combustion gives 2CO2 and 3H2O so hydrocarbon
(a) Physical taste: It is It is solid below 290
‘Z’ must be ethane. “Y’ on addition of H2 gives ethane
liquid. K
so ‘Y’ must be ethene. “X’ in presence of cone. H2SO4
dehydrates to ethene i.e., ‘X’ is ethanol.
(b) Taste: It has It has sour taste.
167. List in tabular form three physical and two chemical burning taste.
properties on the basis of which ethanol and ethanoic
acid can be differentiated. (c) NaHCO3 test It does It liberates CO2 gas.
not react.
Ans : [CBSE 2012]
(d) Ester test: It reacts It reacts with alcohol
Ethanol Ethanoic acid with carboxylic acid to form pleasant to
to form easter form fruity smelling
Physical Properties esters.
1. It has Specific smell It has vinegar (ii)
like smell. CH3CH2OH +
Conc. H 2 SO 4
CH2=CH2 + H2O
443 K
2. It has burnnrg It has sour taste
taste 170. Give reasons for the following:
a. Element carbon forms compound mainly by
covalent bonding.
3. Pure ethanol is liquid Pure acetic b. Diamond has high melting point.
of room temprature. acid is solid c. Graphite is good conductor of electricity.
below 290 K. d. Acetylene bums with sooty flame.
Chemical Properties e. Kerosene does not decolourise bromine water
whereas cooking oil does.
4. It does not It turn-s blue
change colour litmus red. Ans : [CBSE 2011]
of litmus a. It is because carbon can neither lose 4 electrons
nor gain 4 electrons. It can share four electrons to
5. It does not react with It liberstes
form covalent bonds.
NaHCO3 CO2 with
b. Diamond has strong C—C bonds and compact 3-D
NaHC03.
structure in which one carbon atom is covalently
bonded to other four carbon atoms therefore, has
168. What are detergents chemically? List two merits and
high melting point.
two demerits of using detergents for cleansing. State c. In graphite, one carbon atom is bonded to other
the reason for the suitability of detergents for washing three carbon atoms. Remaining one electron on
even in case of water having calcium and magnesium each carbon is free to move due to which graphite
ions. conducts electricity.
Ans : [CBSE 2012] d. Acetylene has high carbon content, therefore,
Detergents are sodium or potassium salts of sulphonic partial oxidation causes it to bum with sooty or
acids of benzene or sulphates of unsaturated smoky flame.
hydrocarbons like alkenes with —SO3Na or —SO4Na e. Kerosene is a saturated compound, therefore,
group. does not decolourise bromine water.
Merits:
They are more effective than soaps.
They work well even with hard water.
Demerits:
a. They are expensive.
b. Some of them create water pollution.

169. a.In a tabular form, differentiate between ethanol

and ethanoic acid under the following heads:
(i) Physical state
(ii) Taste
(iii) NaHCO3 test
(iv) Ester test
b. Write a chemical reaction to show dehydration of
ethanol.
Ans : [CBSE 2011]
(i)
Chap 12 : Electricity www.cbse.online

CHAPTER 12
Electricity

ONE MARK QUESTIONS electric current in a circuit.

(b) How is an ammeter connected in a circuit to
measure current flowing through it?
1. If the charge on an electron be 1.6 # 10-19 C , find the Ans : [CBSE 2015]
approximate number of electrons in 1 C. a. Ammeter is used to measure electric current.
Ans : [CBSE 2016] b. Ammeter is connected in series in an electric
circuit.
1.6 # 10-19 C charge is of = 1 electron and
1 C charge is of = 1 electron
1.6 # 10-19
No. of electrons = 6.25 # 1018

2. List any two factors on which resistance of a conductor

depends.
Ans : [CBSE 2016]
Resistance of a conductor:
a. is directly proportional to its length
R ?r ...(1)
b. is inversely proportional to its area of cross section.
R ? 1 ...(2)
A
Combining (1) and (2), we get 8. In an electric circuit, state the relationship between
r the direction of conventional current and the direction
R ?
A of flow of electrons.
3. What is the SI unit of electric potential? Ans : [CBSE 2015]
Ans : [Delhi 2016] Electrons flows from negative terminal to positive
Volt is the SI unit of electric potential. terminal where as current flows from +ve terminal
to - ve terminal in external circuit i.e. Conventional
4. When is potential difference between two points said current and electrons flow are opposite to each other.
to be 1 volt?
9. How does the resistivity of alloys compare with those
Ans : [Delhi 2016]
of pure metals from which they may have been formed?
Potential difference betweeen two point is said to be Ans : [All India 2014]
1 Volt if the amount of work done in bringing 1 C
charge between them is 1 J. The resistivity of pure metals is lesser than resistivity
of alloys with which these alloys are made.
5. State Ohm’s law.
10. Write SI unit of resistivity.
Ans : [Delhi 2016]
Ans : [CBSE 2014]
If the physical conditions of a conductor remain
same then current through a conductor is directly Ohm-m
proportional to the potential difference b/w the two
11. State a difference between the wire used in the element
ends of the conductor.
of an electric heater and in a fuse wire.
I ? V & V = IR Ans : [CBSE 2014]
6. Mention one reason why tungsten is used for making The wire used in element of electric heater has high
filament of electric lamp. resistance and high melting point where as a fuse wire
Ans : [CBSE 2015] has a low resistance and low melting point.
Tungsten is used for making filament because of its 12. Power of a lamp is 60 W. Find the energy in joules
high melting point and low resistivity. consumed by it in 1 s.
Ans : [CBSE 2014]
7. (a) Name the instrument/device used to measure
 P = 60 W , t = 1 s 19. happens to the resistance of a conductor when the
Energy = ^VI h t length of the conductor is reduced to half?
Ans : [CBSE 2010]
E = P # t = 60 # 1 J
Resistance is directly proportional to the length of the
E = 60 J
conductor. If length becomes half the resistance also
13. Draw a schematic diagram of a circuit consisting of a become half of its initial value.
cell of 1.5 V, 10 ohm resistor and 15 ohm resistor and
20. What happens to the resistance of a conductor when
a plug key all connected in series.
temperature is increased?
Ans : [CBSE 2011]
Ans : [CBSE 2010]
Schematic diagram is shown below.
The resistance of a conductor increases with rise in
temperature.

21. Draw a schematic diagram of an electric circuit

consisting of a battery of two cells each of 1.5 V, 5 W ,
10 W and 15 W resistors and a plug key, all connected
in series.
Ans : [CBSE 2000]
Schematic diagram of electric circuit con¬taining
14. Why do we use copper and aluminium wire for cells, key and three resistances.
transmission of electric current?
Ans : [CBSE 2011]
Copper and aluminium wires are used for electric
transmission due to their low resistivity.

15. Give an example of a metal which is the best conductor

of heat.
Ans : [CBSE 2011 ]
Gold, Silver, Copper etc. metals are good conductor
of heat.
22. Out of the two, a toaster of 1 kW and an electric
16. Define electric circuit. Distinguish between open and heater of 2 kW, which has a greater resistance?
closed circuit. Ans : [CBSE 2006]
Ans : [CBSE 2010] 2
As R = V . If V is constant. Then R ? 1 i.e. more
Electric circuit is the arrangement in which electric P P
current can flow when circuit is switched on. In open power, lesser be the resistance and vice versa.
circuit there is no flow of current as the switch is off. Toaster has lesser power (1 KW) than electric heater
In closed circuit a current flows in the circuit when (2 KW) therefore resistance of toaster is more than
switch is on. resistances of heater.

17. What is the lowest resistance that can be obtained 23. Why is tungsten metal selected for making filaments
by combining four coils of resistances 4 W , 8 W , 12 W of incandescent lamps?
and 24 W ? Ans : [CBSE 2005]
Ans : [CBSE 2010] Tungsten has high resistance and high melting point.
If the resistances are combined in parallel then we
24. A wire of resistance 5 W is bent in the form of a closed
shall get the lowest resistance. In parallel combination:
circle. What is the resistance between two points at
1 = 1 + 1 + 1 + 1 the ends of any diameter of the circle?
R R1 R2 R3 R 4
Ans : [CBSE 2005]
= 1+1+ 1 + 1
4 8 12 24 R = 5W
It can be assumed as two semi circular elements are
= 6 + 3 + 2 + 1 = 12 = 1 connected across diameter AB .
24 24 2
Total resistances of couple wire 5 W . Resistance of two
R = 2W
semicircular elements = 5 W
2
18. Nichrome is used to make the element of electric
Both the elements are connected in parallel.
heater. Why?
Ans : [CBSE 2010] 1 = 1 + 1 =2+2= 4
Rl R1 R2 5 5 5
Nichrome is used to make element of electric heater
because nichrome is an alloy which has high melting or Rl = 5 W
4
point and high resistances.
25. Why is much less, heat generated in long electric
 cables than in filaments of electric bulbs? R = 20 ohm
Ans : [CBSE 2005]
R =rl
A
2
As heat produced = I Rt
Electric cables are made of thick good conductor or r = R A = 20 # 2 W cm
l 10
where as filaments are made of thin tungsten wire
whose resistances is high. The resistance of electric r = 4 W - cm
cables is very less. So heat produced in cable is much
lesser than filaments. TWO MARKS QUESTIONS
26. State which has a higher resistance a 50 W or a 25 W
lamp bulb and how many times?
29. The amount of charge passing through a cell in four
Ans : [CBSE 2005] second is 12 C. Find the current supplied by cell.
We have P1 = 50 W Ans : [CBSE 2016]
P2 = 25 W Given: t =4s
Let their resistances are R1 and R2 respectively.
Q = 12 C
2 2
P = V or R = V Q
R P I = = 12 A = 3 A
t 4
2 2
R1 = V W and R2 = V W
50 25 30. Calculate the number of electrons that would flow per
R1 = 25 = 1 second through the cross- section of a wire when 1 A
R2 50 2 current flows in it.
Ans : [CBSE 2016]
or R1 = 1 R2
2
Given: I = 1 A, t = 1 s
1
i.e. 50 W bulbs has resistance than 25 W bulb.
2 Q
I = & Q = I#t
t
27. Define resistivity of a material.
Ans : [CBSE 2004] Q = 1A#1s (Q = 1 coulomb)
But Q = ne
We have R =rl Q
A n = = 1C
e 1.6 # 10-19
Resistivity, r = RA
l = 6.25 # 1018 electrons
If
A = 1, l = 1 then r = R i.e. resistivity of a material 31. Name the device/instrument used to measure potential
is the resistance of a conductor of this material whose difference. How is it connected in an electric circuit?
length and area of cross- section both are unity.
Ans : [CBSE 2016]
or
Resistivity of a material is the resistance of a conductor The device which is used to measure potential
of this material whose volume is unity. difference is voltmeter. Voltmeter is connected in
parallel in an electric circuit.

32. How much current will an electric bulb of resistance

1100 W draw from a 220 V source? If a heater of
resistance 100 W is connected to the same source
instead of the bulb, calculate the current drawn by
the heater.
Ans : [All India 2016]

Resistance of bulb, R = 1100 W

V = 220 volt
V = IR or I = V
R

I = 220 = 1 A
1100 5
28. A cylinder of a material is 10 cm long and has a cross- When heater is connected with the same source then
section of 2 cm2. If its resistance along the length be
20 ohm, what will be its resistivity in number and I = V = 220 = 2.2 A
R 100
units?
Ans : [CBSE 2004] 33. (a) What are the values of mA and mA ?
(b) Draw the symbols of battery and rheostat.
l = 10 cm, A = 2 cm2 Ans : [All India 2015]
 1 mA = 1 milli ampere = 10-3 A A — Bulb (load)
1 mA = 1 micro ampere = 10-6 A B — Rheostat
C — Cell
D — Ammeter (being in series)

34. Give reason for the following:

a. Tungsten used almost exclusively for filament of
electric lamp.
b. Why do we use copper and aluminium wires for
transmission of electric current?
Ans : [CBSE 2015]
a. Tungsten is used in making the filament of
electric lamp because it has high resistivity and 39. A large number of free electrons are present in metals
high melting point. yet no current flows in the absence of electric potential
b. The copper and aluminium have low resistivity across it. Explain the statement with reason.
and high conductivity. Ans : [CBSE 2014]
35. What is the resistance of an ideal voltmeter? Though there are large number of free electron present
Ans : [CBSE 2014] in a conductor, but their motion is random motion
in the absence of potential difference. Their average
The resistance of an ideal voltmeter is infinite. velocity is zero. Hence there is no current flowing in
36. State the factors on which the heat produced in a conductor. But when a potential difference is applied
current carrying conductor depends. Give one practical across the ends of the conductor, it sets the electrons
application of this effect. to move in a direction. The motion of charge produces
an electric current in the conductor.
Ans : [Delhi 2014]
We know that H = VIt or H = I2 Rt 40. Out of the two wires X and Y shown below. Which
Heat produced in a current carrying conductor one has greater resistance. Justify your answer.
H ? I2 (Square of the current in the circuit)
? R (Resistance of the conductor)
? t (Time for which current is passed in conductor)
This effect applied in electric heater.

37. List in a tabular form two differences between a

voltmeter and an ammeter. Ans : [CBSE 2014]
Ans : [CBSE 2014] If X and Y are of same material
then length of wire X = l
Voltmeter Ammeter
Area of cross-section = A
1. It is used to It is used to
measure P.D. across measure electric RX = r l
A
two points in an current in an
electric circuit. electric circuit. Similarly, RY = r 2l
A
2. Its resistance is very Its resistance is RY = 2
high. very low. RX
3. An voltmeter An ammeter is or RY = 2RX
is connected in connected in series wire Y has two times resistance than that of wire X .
parallel in an in an electric
electric circuit. circuit. 41. Elements of electric toasters and electric iron are
made of an alloy rather than a pure metal. Give two
reasons to justify the statement.
38. Given below is a circuit showing current flowing in it.
Identify each component A, B, C, D of this circuit. Ans : [CBSE 2014]
a. Alloys have higher resistivity than their
constituents pure metals.
b. At high temperature alloys do not oxidise.

42. A thick wire and a thin wire of the same material

are successively connected to the same circuit to find
their respective resistance. Which one will have lower
resistance? Give reason.
Ans : [CBSE 2014]
Ans : [CBSE 2014]
1
As resistance ? i.e. more area of cross-section lesser
Circuit A
 the resistance and vice versa. So thick wire has lower ends of the conductor, charges (electrons) will move
resistance. in the conductor.
Potential difference is applied by a cell to maintain
43. Mention two special features of the material to be the charge to move.
used as element of an electric iron.
Ans : [CBSE 2014] 48. How would the reading of voltmeter (V) change, if it
is connected between B and C? Justify your answer.
A material to be used as element of an electric iron
must have (i) high melting point, (ii) high resistivity.

44. Find the resistance of bulb rated as 100W-250V.

Ans : [CBSE2014]

We have, P = 100 W
V = 250 Volt
2 2
P = V or R = V
R P Ans : [CBSE 2011]
^250h2
1W, 3W, 2W resistances are connected in series.
R = = 250 # 250 = 625 W
100 100
R = R1 + R2 + R3
45. Why do the wires connecting an electric heater to the = 1+3+2 = 6W
mains not glow while its heating element does?
I =V = 3 = 1A
Ans : [CBSE 2011] R 6 2
Connecting wire has low resistivity or good Current in each resistance is same, i.e. 1 A .
2
conductivity, i.e. resistance of these wires is negligible
Voltage across B & C = 1 # 3 = 3 Volt.
hence no heat is produced while heating element 2 2
is of an alloy whose resistivity is high, due to high
resistance heat is produced in the element. VBC = 3 Volt.
2
46. In the circuit diagram shown, the two resistance wires
A and B are of same area of cross-section and same
material, but A is longer than B. Which ammeter A1
or A2 will indicate higher reading for current? Give
reason.

49. In the circuit diagram shown, the two resistance wires

A and B are of same length and same material, but
A is thicker than B. Which ammeter A1 or A2 will
indicate higher reading for current? Give reason.

Ans : [CBSE 2011]

Length of A is greater than B. Area of cross-section of
A and B is same.
Therefore resistance of A 2 resistance of B 6a R ? l @ .
Current in A is lesser than current in B. Hence A2 will
give higher reading.
Ans : [CBSE 2011]
Length of A and B is same. A is thicker than B.
Hence RA < RB ;a R ? 1 E
A
Current in A1 is more than current in A2 i.e., reading
in A1 is higher than reading in A2.

47. Mention the condition under which charges can move

in a conductor. Name the device which is used to
maintain this condition in an electric circuit.
Ans : [CBSE 2012]
When a potential difference is applied across the two
50. Tungsten is used almost exclusively for filaments of a. Tungsten is used in making filament.
electric bulb. List two reasons. b. Its high resistivity and high melting point.
Ans : [CBSE 2011]
54. How are ammeters and voltmeters connected in a
(1) high resistivity (2) high melting point and does circuit? What do they help us measure?
not oxidise at very high temperature. Ans : [CBSE 2010]
51. Three V-I graphs are drawn individually for two An ammeter which measure the current in a circuit
resistors and their series combination. Out of A, B, C is connected in series. Voltmeter is used to measure
which one represents the graph for series combination potential difference across a conductor so it is
of the other two. Give reason connected in parallel to it.

55. The following table gives the resistivity of three

samples:

Sample A B C
Resistivity 1.6 # 10 Wm 5.2 # 10 Wm 100 # 10-4 Wm
-5 -5

Which of them is suitable for heating elements of

electrical appliances and why?
Ans : [CBSE 2010]
Ans : The resistivity of C sample is maximum so it is
More slope of V-I graph means more resistance, slope suitable for making heating element.
of C is maximum. Hence its resistance is maximum.
So it is for series combination of two resistors. 56. a. Give reason why tungsten is used for making
filament of electric lamps.
b. The elements of heating electrical appliances are
made-up of an alloy rather than pure metal.
Ans : [CBSE 2010]
a. Due to (1) high resistivity and high melting point
tungsten is used for making filaments of electric
lamp.
b. high resistivity, and high melting point than their
constituents pure metals which do not oxidise at
high temperature.
52. State the factors on which the resistance of a cylindrical
conductor depends. How will resistance of a conductor 57. B1, B2 and B3 are three identical bulbs connected as
change if it is stretched so that its length is doubled? shown in the figure. When all the three bulbs glow, a
current of 3 A is recorded by the ammeter A.
Ans : [CBSE 2010]
a. What happens to the glow of the other two bulbs
Resistance of cylindrical conductor depends upon its when the bulb B1 gets fused?
length and cross- sectional area. b. What happens to the reading of A1 A2, A3 and A
When conductor is stretched its radius decreases but when the bulb B1 gets fused?
the volume of the conductor in both the cases will be
same. If length is stretched to twice.
l2 = 2l1
As l1 A1 = l2 A2
l1 A1 = 2l1 A2
A1 = 2
A2
Now, R1 = r l1
A1

and R2 = r l2 = r 2l1
A2 A2
Ans : [CBSE2010]
R2 = 2 A1 = 2 2 = 4
R1 #A
2
# a. The other two bulbs will glow even if B1 gets
fused. There is no change in glow of B2 and B3.
R2 = 4R1
Here V = 4.5 V
53. (a) What material is used in making the filament of and I = 3A
an electric bulb?
(b) Name the characteristics which make it suitable RP = V = 4.5
I 3
for this.
R P = 1. 5 W
Ans : [CBSE 2010]
For parallel combination
 1 = 1 + 1 + 1 Q
RP R1 R2 R3 I = or Q = I # t
t
1 = 1+1+1 Q = 0.2A # 1 hr = 0.2 # 60 # 60 A - s
1.5 R R R
= 720 C
1 = 3 & R = 4. 5 W
1.5 R 61. An electric iron draws a current of 0.5 A when the
For B 2 , 4.5 = I # 4.5 voltage is 200 volt. Calculate the amount of electric
charge flowing through it in one hour.
1A = I
Ans : [CBSE 2004]
For B 3 , 4.5 = I # 4.5 1A = I
Current in Ammeter, ^Ah = 1A + 1A = 2A We have I = 0.5 A
V = 200 volt
t = 1 hr = 3600 s
Q = I # t = 0.5 # 3600 A - s = 1800 C

62. An electric appliance draws a current of 0.4 A when

the voltage is 200 volt. Calculate the amount of charge
flowing through it in one hour.
Ans : [CBSE 2004]

Q = It
58. (a) Draw a circuit diagram to show how two resistors Given, I = 0.4 A
are connected in series.
V = 200 Volt
(b) In a circuit, if the two resistors of 5 ohm and 10
ohm are connected in series, how does the current t = 1 hr = 3600 s
passing through the two resistors compare? ` Q = 0.4 # 3600 C
Ans : [C8SE 2006) Q = 1440 C

THREE MARKS QUESTIONS

a.
63. Show how would you join three resistors, each of
resistance 9 W so that the equivalent resistance of the
b. In series combination of resistances, the current combination is (i) 13.5 W (ii) 6 W ?
remains same. Ans : [CBSE 2017]
or
59. A bulb is rated at 5.0 V, 100 mA. Calculate its (a)
(a) Write Joule’s law of heating.
power and (b) resistance.
(b) Two bulbs, one rated 100 W; 220 V, and the other
Ans : [CBSE 2006] 60 W; 220 V are connected in parallel to electric
mains supply. Find the current drawn by two
Rating of bulb, V = 5.0 Volt.
bulbs from the line if the supply voltage is 220 V.
I = 100 mA Ans : [CBSE 2017]
I = 100 # 10-3 A
I = 0.1 A
a. Power of bulb = V # I i.

P = 5.0 # 0.1 W = 0.5W

Resistor R2 and R3 are in parallel combination.
b. V = IR , 1 =1+1 =2W
`
R = V = 5.0 W = 50 W Rp 9 9 9
I 0. 1
or Rp = 9 W
2
60. An electric bulb draws a current of 0.2 A when the
voltage is 220 volts. Calculate the amount of charge
flowing through it in one hour.
Ans : [CBSE 2004] Now R1 and R p are in series.
Given: I = 0.2 A ` Req = R1 + R p = 9 + 9 = 27 W
2 2
V = 220 Volt Req = 13.5 W
t = 1 hr. ii. To get 6 W resistance R1 and R2 are in Series

Q =? ` Rs = 9 + 9 = 18 W
 Rs and R3 are in parallel so, resistance of A is more and its length also.
1 = 1 + 1
Req. Rs R3
1 = 1 +1 = 1+2 = 3
Req. 18 9 18 18
and Req. = 6 W

66. What is meant by “electrical resistance” of a

or conductor? State how resistance of a conductor is
a. Joules Law of Heating : When a current I is affected when
passed through a resistor R for time t then heat a. a low current passes through it for a short
produced duration;
b. a heavy current passes through it for about 30
H ? I2
seconds.
?R Ans : [CBSE 2016]
?t
Electrical resistance is the property of a conductor by
H ? I2 Rt virtue of which it opposes the flow of current through
or H = I2 Rt it. It is equal to the ratio of the potential difference
b. Given two bulbs of 100 W–200 V and 60W–220 V. applied across its ends to the current flowing through
Current in 1st bulb: it.

I1 = P1 = 100 A = 5 = 0.45 A R =V
V 220 11 I
a. When a low current is passed for a short duration,
Current in second bulb. through a conductor, heat produced is almost
negligible and hence no appreciable change in its
I2 = P2 = 60 A = 3 A = 0.27 A
V 220 11 resistance.
b. When heavy current is passed through the
64. (a) List the factors on which the resistance of a conductor for 30 s. Conductor may be get heated
conductor in the shape of a wire depends. and its resistance and resistivity change.
(b) Why are metals good conductors of electricity
whereas glass is a bad conductor of electricity? 67. Name and define the SI unit of current. Calculate the
Give reason. number of electrons that flow through a conductor in
(c) Why are alloys commonly used in electrical 1 second to constitute a current of 1 ampere. (Charge
heating devices? Give reason. on an electron = 1.6 # 10-19 coulomb)
Ans : [CBSE 2017] Ans : [CBSE 2016]
a. Factors on which resistance of a wire depends: SI unit of current is Ampere (A)
i. Resistance is directly proportional to length. q
ii. Resistance is inversely proportional to area of I =
t
cross-section. If q = 1 C, t = 1 s
then I = 1A
R ? l, R ? 1 If 1 C charge flows in 1 s in a conductor then magnitude
A
of current is said to be 1A.
R ? l or R = r l
A A q = ne
b. Metal are good conductor due to having large q
n = = I#t
number of free electrons and their low resistivity. e e
Glass is a bad conductor because it has no free
electrons and its resistivity is higher. = 1A # 1-s19 = 100 # 1018
1.6 # 10 16
c. Alloys are commonly used in electrical heating
devices due to their high resistivity and high = 6.25 # 1018
melting point which produces more heat.
68. Electric current flows through three lamps when
65. V-I graphs for two wires A and B are shown in the arranged in (a) a series (b) a parallel. If the filament
figure. If both the wires are made of the same material of one lamp breaks. Explain what happens to the
and are of equal thickness, which of the two is of more other two lamps in both the cases.
length? Give justification for your answer. Ans : [CBSE 2015]
Ans : [CBSE 2016] a. In series combination if the filament of one lamp
We know for identical wire more length more resistance breaks then the circuit will be broken and hence
and vice versa slope of wire A is more than B. Hence other lamps stops glowing.
 work is done.
Ans : [All India 2015]

Given: V = 20 Volt
W = 40 J
W = P#t
= V#I#t
b. In parallel combination of lamps if the element of Q
= V# #t
one lamp breaks then other two will continue to t
glow. or W = V#Q
40 = 20 # Q
or Q = 2C
ne = Q
Q 2
n = =
e 1.6 # 10-19
= 1.25 # 1019

71. Name and define SI unit of resistance. Calculate the

resistance of a resistor if the current flowing through
it is 200 mA, when the applied potential difference is
69. Study the V-I graph for a resistor as shown in the 0.8 V.
figure and prepare a table showing the values of I (in Ans : [Delhi 2014]
amperes) corresponding to four different values of V
a. SI unit of resistance is ohm ^Wh
(in volts). Find the value of current for V = 10 volts.
How can we determine the resistance of the resistor 1W = 1V
1A
from this graph?
b. The resistance of a conductor is said to be 1 ohm
if a current of one amp flows through it when a
potential differences of 1 volt is applied across it.
c. R = V = 0.8 =4W
I 200 # 10-3

72. (a) Explain why a conductor offers resistance to the

flow of current.
(b) Differentiate between conductor, resistor and
resistance.
Ans : [CBSE2014]
Ans : [CBSE 2015] a. When a current is passed through a conductor,
When V = 10 volt from the graph the atoms or molecule of the conductor produce
an hindrance in the path of flow of electron. This
R = TV = 8 - 6 W = 2 W hindrance in the path of flow of charge is called
TI 4-3
resistance of the conductor.
b. A substance which allow to pass the charges
through them easily is called a conductor.
Resistor : A conductor having some value of
resistance is called a resistor.
Resistance : It is the property of any conductor
by virtue of which it opposes the flow of charge
through it.

73. A piece of wire of resistance 6 W is connected to battery

of 12 V. Find the amount of current flowing through
it. Now, the same wire is redrawn by stretching it
when V = 10 volt to double its length. Find the resistance of the new
(redrawn) wire.
then V = IR
Ans : [CBSE2014]
or I = V = 10 A = 5A
R 2 Given: R = 6W
V = 12 Volt
70. Find the number of electrons transferred between two
points kept at a potential difference of 20 V if 40 J of I =?
 I = V = 12 A & I = 2A
R 6 R 2 = 7. 5 W
When length becomes twice = 2 L
76. Find the equivalent resistance of the following circuit:
area of cross-section = A2
then L1 A1 = L2 A2
or LA1 = 2LA2
or A2 = 1
A1 2

R1 = r L
A1

R2 = r 2L & R2 = 2 # A1
A2 R1 A2 Ans :
R2 = 2 2 = 4
R1 #
In the given circuit 2 W, 2 W resistances are in parallel.
R2 = 4R1 Rp = 1 W
New resistance becomes four times.

74. A wire of length l and resistance R is stretched so

that the length is doubled and area of cross-section is
halved. How will its:
a. Resistance change?
b. Resistivity change?
Ans : [CBSE 2010, 2014]
a. Let initial length, area of cross-section and
resistance of wire are l , A and R respectively. 1W, 1W resistances also are in parallel.
When length is stretched two times, let its area Rl
p = 0.5 W
of cross-section becomes Al. Its initial volume of The circuit can be reduced as,
wire = final volume of the wire.
Al = Al2l
or Al = 1 or Al = A
A 2 2
^2l h
Rl = r = r 2l # 2
Al A

= 4r l Now all resistances are in series combination.

A
=4R R = 3 + 3 + 1 + 0.5 = 7.5 W
b. Resistivity does not change because it is property
77. A hot plate of an electric oven connected to a 220 V
of the material of a conductor.
line has two resistors A and B each of 22 W resistance.
75. A nichrome wire has a resistance of 10 W Find the These resistors may be used separately, in series or
resistance of another nichrome wire, whose length is in parallel. Find the current flowing in all the three
three times and area of cross-section four times the cases.
first wire. Ans : [CBSE 2014]
Ans : [CBSE 2014]
Given, V = 220 Volt
We have R = 10 W RA = 22 W
l1 = l RB = 22 W
A1 = A a. Current in resistances separately?

R = r l = 10 W = 220 A = 10 A
A 22
b. Current in series combination
or l = 10
A r RS = 22 + 22 = 44 W
For new wire,
IS = 220 = 5 A
L2 = 3l 44
c. Current in parallel combination
A2 = 4A
1 = 1 + 1 = 2 W
R2 = r 3l = 3 r l RP 22 22 22
4A 4 A
& RP = 11 W
R2 = 3 R = 3 # 10 = 15 W
4 4 2
 IP = 220 = 20 A so first bulb will consume more energy.
11
81. Draw the nature of V–I graph for a nichrome wire. (V
78. An electric kettle of 2 kW works for 2 h daily. Calculate -Potential difference, I -Current)
the (a) energy consumed in SI and commercial units A metallic wire of 625 mm length offers a 4 W
(b) cost of running it in the month of June at the rate resistance. If the resistivity of the metal is 4.8 # 10-7
of ` 3.00 per unit. ohm-metre, then calculate the area of cross-section of
Ans : [CBSE 2014] the wire.
Ans : [CBSE 2013]
(a) Given: P = 2 kW = 2000 W
V–I graph for nichrome wire
t = 2h
Electric energy, E = P # t = 2 # 2 = 4 kWh
(b) Total energy consumed in month of June (having
30 days)
Electric kettle = ^4 # 30h kWh = 120 kWh
= 120 units.
Cost of running electric kettle:
= `120 # 3 = `360

79. Two lamps, one is rated 100 W at 220 V, and the Given: l = 625 mm = 0.625 m
other 60 W at 220 V, are connected in parallel to a
R =4W
220 V supply. Find the current drawn from the supply
line. r = 4.8 # 10-7 Ohm-m
Ans : [CBSE 2014] A =?
Given: Lamp one 100 W, 220 V, Lamp 2 60 W, 220 V. R = r l or A = r l
Let their resistances are R1 and R2 A R
2 A = 4.8 # 10-7 # 0.625
R =V 4
P
= 0.75 # 10-7 m2
R1 = 220 # 220 W = 484 W
100
82. Derive the relation R = R1 + R2 + R3 when three
= 220 # 220 W = 2420 W resistors R1, R2 and R3 are connected in series in an
60 3 electric circuit.
In circuit R1 and R2 are connected in parallel. Ans : [CBSE 2012]
1 = 1 + 3 Three resistors R1, R2 and R3 are connected in series.
R 484 2420 Therefore current in each resistor is same. Let current
in the circuit is I.
R = 605 W
2

I = V = 220 # 2 A = 0.727 A
R 605

80. Two bulbs A and B are rated as 90W–120V and

60W–120V respectively. They are connected in parallel
across a 120V source. Find the current in each bulb.
Which bulb will consume more energy?
Ans : [CBSE 2014] Applied total potential = Sum of the potentials across
each resistor
First Bulb: 90 W–120 V
2 V = V1 + V2 + V3
R1 = V = 120 # 120 = 160 W IReq = IR1 + IR2 + IR3
P1 90
Req = R1 + R2 + R3
I1 = V = 120 = 0.75 A
R1 160
83. (a) Nichrome wire of length L and radius R has
Second Bulb: 60W–120V resistance of 10 Q. How would the resistance of
2 the wire change when:
R2 = V = 120 # 120 (i) Only length of the wire is doubled?
P2 60
(ii) Only diameter of the wire is doubled? Justify
R2 = 240 W your answer.
I2 = V = 120 (b) Why element of electrical heating devices are
R2 240 made-up of alloys?
I2 = 0.5A Ans : [CBSE 2012]
Power of first bulb has more power than second bulb,
 a. R = 10 W of length L, and area of cross-section A. b. We know that R = r l
i. When only length is doubled Rl = 20 W A
ii. When only diameter is doubled. r ?A
R ? 1 ? 12 Thicker the wire, more the resistivity. The
A D resistivity of manganin is more than copper. So
1 manganin wire is thicker than copper.
Rll ?
^2D h2
87. Two conducting wires of same material, equal length
Rll ? 1 2 and equal diameter are connected in series. How does
4D
the heat produced by the combination of resistance
Rll = R change?
4
Ans : [CBSE 2010]
Rll = 10 = 2.5 W Let the resistances of two wires are R each.
4
Heat produced by individual resistor
b. Alloys have high resistivity more than their
2
constituent pure metals and do not oxide at high Hl = V t
temperature easily. R
Resistance is series, RS = R + R = 2R
84. Resistivity of two elements A and B are
Heat produced by combination of resistors
= 1.62 # 10 Wm and 520 # 10-8 Wm respectively.
-8
2
Out of these two, name the element that can be used Hl = V t
to make: 2R
a. filament of electric bulb. Hl = 1
b. wires for electrical transmission lines. Justify your H 2
answer in each case.
Hl = H
Ans : [CBSE 2012] 2
88. Study the following circuit and answer the following
Given: r A = 1.62 # 10-8 Wm
questions:
r B = 520 # 10-8 Wm
a. For filament of electric bulb resistivity must be
higher i.e. 520 # 10-8 Wm . So element B is used
for filament.
b. For electric transmission resistivity must be lower
which is of element A.

85. State Ohm’s law. Calculate the resistance of a

conductor, if the current flowing through it is 0.2 A
when the applied potential difference is 0.8 V. a. State the type of combination of the two resistors
Ans : [CBSE 2012] in the circuit.
If the physical conditions of a conductor are kept same b. How much current would flow through: (1) 10 W
then current is directly proportional to the potential resistor and (2) 15 W resistor?
difference across the ends of the conductor V ? I . c. What would be the ammeter reading?
V = RI Ans : [CBSE 2010]
I = 0.2 A a. 10 W and 15 W are in parallel combination.
b. Potential difference across each is 3V.
V = 0.8 Volt.
R =? I in 10 W resistor = 3 = 0.3 A
10
R = V = 0.8 W I in 15 W resistor = 3 = 0.2 A
I 0.2 15
R =4W I = 0.3 + 0.2 = 0.5 A
86. (a) Why are copper or aluminium wires generally 89. Define electric current and state its SI unit. With
used for electrical transmission and distribution the help of Ohm’s law explain the meaning of 1 Ohm
purposes? resistance.
(b) Two wires, one of copper and other of manganin,
Ans : [CBSE 2010]
have equal lengths and equal resistances. Which
wire is thicker? Given that resistivity of copper is Electric current may be defined as the rate of flow of
lower than that of manganin. charge through a circuit. Its SI unit is Ampere.
Ans : [CBSE 2011] According to Ohm’s law V = IR

a. Copper or aluminium wires are used for R =V

I
transmission and distribution of electricity due to
their low resistivity and high conductivity. If V = 1 Volt, I = 1 A then R = 1 ohm.
A conductor has a resistance of 1 Ohm if a current of
 one amp flows through it when a potential difference P = 100 W
of 1 volt is applied across it. 4
P = 25 W
90. (a) What is the total resistance of n resistors each of
resistance ‘R’ connected in: (i) series? (ii) parallel? 92. (a) How is the direction of electric current related to
(b) Calculate the resultant resistance of 3 resistors the direction of flow of electrons in a wire?
3 W, 4 W and 12 W connected in parallel. (b) Calculate the current in a circuit, if 500 C of
Ans : [CBSE 2010] charge passes through it in 10 minutes.
a. In series combination Ans : [CBSE 2009]
RS = R1 + R2 + ....Rn a. The direction of flow of electrons is opposite to
RS = R + R.....n times the direction of conventional current.
b. Q = 500 C , t = 10 mts = 10 # 60 = 600 s
RS = nR
Q
In parallel combination: I = = 500 A
t 600
1 = 1 + 1 + ..... 1
RP R1 R2 Rn I = 0.83 A

= 1 + 1 + 1 + ..... + n times 93. (a) Define the term ‘volt’.

R R R (b) State the relation between work, charge and
= 1 + 1 + .....n times potential difference for an electric circuit.
R Calculate the potential difference between the
1 =n two terminals of a battery, if 100 joules of work
or
RP R is required to transfer 20 coulombs of charge from
one terminal of the battery to the other.
RP = R Ans : [CBSE 2009]
n
b. Given:
a. Potential difference b/w two points in an electric
R1 = 3 W
field is said to be 1 volt if the amount of work
R2 = 4 W done in bringing a unit positive charge from one
R3 = 12 W point to another point is 1 J.
b. Given: W = 100 J , Q = 20 C , V = ?
1 = 1 + 1 + 1
R R1 R2 R3 As V = W & V = 100 JC-1
Q 20
=1+1+ 1
3 4 12 V = 5 JC-1

= 4+3+1 = 8 = 2 V = 5 Volt.
12 12 3
94. State the formula co-relating the electric current
R = 3 W = 1.5 W flowing in a conductor and the voltage applied across
2
it. Also, show this relationship by drawing a graph.
91. (a) State Ohm’s law. Express it mathematically. What would be the resistance of a conductor, if
(b) Write symbols used in electric circuits to represent: the current flowing through it is 0.35 ampere when the
(i) variable resistance. potential difference across it is 1.4 volt?
(ii) voltmeter. Ans : [CBSE 2004]
(c) An electric bulb is rated 220 V and 100 W. When
it is operated on 110 V, what will be the power V = IR
consumed?
i.e., V ?I
Ans : [CBSE 2010] If we plot a graph b/w V and I , it is straight line.
a. Ohm’s Law states that if the physical conditions of Graph b/w V and I :
a conductor are kept constant then current passing
through a conductor is directly proportional to
the potential difference across its ends.
V ? I or V = RI
b. A variable resistor
c. Given rating of bulb 220 V – 100 W
R=?
Power consumed = ? when V = 110 Volt Given: I = 0.35 A
2 V = 1.4 Volt.
R = V = 220 # 220 = 484 W
P 100
R = V = 1.4 Ohm
Power at 110 volt I 0.35
2
P = V = 110 # 110 R =4W
R 484
 FIVE MARKS QUESTIONS

95. The value of current (I) flowing through a given

resistor of resistance (R), for the corresponding values
of potential difference (V) across the resistor are as The work done in bringing a charge Q from one
given below : end to another of the conductor
V 0.5 1.0 1.5 2.0 2.5 3.0 4.0 5.0 W = QV
I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Q
But =I
t
Plot a graph between current (I) and potential
difference (V) and determine the resistance (R) of the Q = It
resistor. W VIt
Ans : [CBSE 2018] b. 40 W–240 V 25 W–240 V
2 2
P1 = V 1 R2 = V 2
R1 P2
2
R1 = V 1 R2 = 240 # 240 W
P1 25

R1 = 240 # 240 W
40
R1 = 25 or R1 = 5
R2 40 R2 8
R1 < R2 i.e., Resistance of 25 W bulb is more than 40
W bulb.

96. Draw a labelled circuit diagram showing three resistors 98. a. What is meant by saying that the potential
R1, R2 and R3 connected in series with a battery difference between two points is 1 volt?
(E), a rheostat (Rh), a plug key (K) and an ammeter b. Why does the connecting cord of an electrical
(A) using standard circuit symbols. Use this circuit to heater not glow while the heating element does?
show that the same current flows through every part c. Electrical resistivity of some substance at 20°C
of the circuit. List two precautions you would observe are given below:
while performing the experiment.
Silver 1.60 # 10-8 Wm
Ans : [CBSE 2016]
By changing the position of ammeter, measure the
Copper 1.62 # 10-8 Wm
current in it. Every time the magnitude of current is Tungsten 5.2 # 10-8 Wm
found same i.e., in series combination the current in
every part of the circuit, remains same.
Iron 10.0 # 10-8 Wm
Mercury 94.0 # 10-8 Wm
Nichrome 100 # 10-6 Wm
Answer the following questions in relation to them:
i. Among silver and copper which one is better
conductor? Why?
ii. Which material would you advise to use in
electrical heating device? Why?
Ans : [CBSE 2016]
Precaution: a. If the amount of work done in bringing a unit
a. Connect the ammeter in series with battery. positive charge from one point to another is 1 J in
b. All connection must be tight. an electric field then potential difference b/w the
c. Current must not be greater than the two points is said to be 1 volt.
range of ammeter.
1V = 1J
1C
97. (a) Derive the formula for the calculation of work b. Connected cord of an electrical heater does not
done when current flows through a resistor. glow because this is of copper metal, which has
(b) One electric bulb is rated 40 W and 240 V and low resistivity and good conductivity. Heating
other 25 W and 240 V. Which bulb has higher element glows due to its high resistivity or poor
resistance and how many times? conductivity.
Ans : [CBSE 2016] c. (i) The resistivity of silver is lesser than copper so
a. Let R is the resistance of the resistor in which I it is a good conductor.
current is passed for a time t by applying a p.d. ( (ii) The resistivity of nichrome is maximum in the
V ) across the resistor. given table so nichrome will be advised to use
 in electrical heating device. of charge and work. Draw the circuit symbols for
(i) variable resistor, (ii) a plug key which is closed
99. (a) Name an instrument that measures electric one.
current in a circuit. Define unit of electric current. (b) Two electric circuits I and II are shown below “
(b) What are the following symbols mean in an
electric circuit?

(i) (ii)
(c) Draw a closed circuit diagram consisting of 0.5 m
long nichrome wire XY, an , ammeter, a voltmeter,
four cells of 1.5 V and a plug key.
Ans : [CBSE 2015]
a. Ammeter. (i) Which of the two circuits has more resistance?
If IC charge flows in an electric circuit is 1 s then (ii) Through which circuit more current passes?
the current is said to be 1 A. (iii) In which circuit, the potential difference
b. (i) Rheostat (ii) Closed key across each resistor is equal?
(iv) If R1 > R2 > R3 in which circuit more heat
will be produced in R1 as compared to other
two resistors?
Ans : [CBSE 2014]
c.
a. Voltmeter
The amount of work done in bringing a unit
positive charge from one point to another in an
electric field is said to be potential difference

100. What is meant by resistance of a conductor? Name V =W

Q
and define its SI unit. List the factors on which
the resistance of a conductor depends. How is the (i) Variable resistance
resistance of a wire affected if:
a. its length is doubled, (ii) Closed key.
b. its radius is doubled? b. (i) In series combination resistance is more than
Ans : [CBSE 2015] parallel combination.
Property of any conductor by virtue of which it (ii) Lesser the resistance more the current in
opposes the flow of current in the conductor is called circuit i.e., in parallel (II) current is max.
its resistance. (iii) In parallel combination (II)
SI unit of resistance is Ohm. If by applying a potential (iv) More heat in (I) across R1.
difference of 1 volt the current in the conductor is 1 A.
103. When a high resistance voltmeter is connected directly
Then the resistance of the conductor is said to be 1 ohm.
across an electric bulb, its reading is 2 V. An electric
Factor affecting resistances:
cell is sending the current of 0.4 ampere (measured by
a. If length is double then resistance also becomes
an ammeter) in the electric circuit.
doubled.
a. Draw the circuit.
b. If radius is doubled then area A = p ^2r h2 becomes
b. Find the resistance of the electric bulb,
4 times, then the resistance becomes 1/4.
c. State the law that is applied for making these
101. What do you mean by heating effect of electric current? calculation. If a graph is plotted between V and I,
Explain the production of heat in a resistor by flow of show the nature of the graph obtained.
electric current through it. Name two devices based on Ans : [Delhi 2014]
heating effect of current.
Ans : [All India 2015]
When current is passed through a conductor, heat
a.
is produced. Production of heat in a conductor on
passing the current is called heating effect of current.
When a current is passed in a conductor by applying
a potential difference, electrons get accelerated and
collide with the atoms of the conductor. During the
collision there is a loss of kinetic energy. This loss b. V = 2 Volt, I = 0.4 A
in K.E. appears in the form of heat energy in the
conductor 1. Electric heater, 2. Bulb. R = V = 2 ohm or R = 5 ohm
I 0.4
102. (a) Name an instrument that measures potential c. Ohm’s law: If the physical conditions of a conductor
difference between two points in a circuit. Define is kept constant then current in the circuit is
the unit of potential difference in terms of SI unit directly proportional to the potential difference
 applied across the ends of the conductor.

Ans :
a. Potential difference b/w the two terminals of a
cell is produced due to chemical reaction in the
cell. This potential difference maintains a current
Since V ? I
in the circuit.
Hence graph between V and I is a straight line
b. (i) The resistance b/w XZY and XTY are in
for a conductor. Which passes through the origin
parallel combination. Their equivalent resistance.
O of the graph.
1 =1+1
Rxy 2 6
104. Draw a schematic diagram of an electric circuit (in the
“on” position) consisting of a battery of five cells of 2 Rxy = 3 = 1.5 W
2
V each, a 5 W resistor, a 8 W resistor, a 12 W resistor
and a plug key, all connected in series. An ammeter (ii) Net resistance of the circuit
is put in the circuit to measure the electric current R = 1.5 + 1.5 = 3.0 W
through the resistors and a voltmeter is connected so
as to measure the potential difference across the 12 Hence, I =V = 6
R 3
W resistor.
Calculate the reading shown by the: (a) ammeter (b) I = 2.0 A
voltmeter in the below electric circuit. (iii) P.D. across X, Y points
Ans : [CBSE 2014] V = IRxy = 2 # 1.5 = 3.0 V
Resistors of 5 W , 8 W , 12 W all the connected in series. I in 2 W resistor = 3.0 = 1.5 A
Hence, 2

RS = R1 + R2 + R3 I in 6 W resistor = 3.0 = 0.5 A

6
= ^5 + 8 + 12h W
106. (a) State the commercial unit of electric energy and
RS = 25 W find its relation with its SI unit.
As V = IR (b) The current through a resistor is made three
times its initial value. Calculate how it will affect
I = V = 10 A the heat produced in the resistor.
R 25
(c) Find the increase in the amount of heat generated
I = 0.4 A in a conductor if another conductor of double
a. Ammeter reading is 0.4 A. resistance is connected in the circuit keeping all
other factors unchanged.
Ans : [CBSE 2014]
a. Commercial unit of electric energy = kWh
1 kWh = 3.6 # 106 J
b. Initial heat generated in the
resistor = I2 Rt
H1 = I2 Rt ...(1)
when current is made three times i.e. 3I now heat
b. V = IR generated
Potential drop across 12 W resistance
H2 = ^3I h2 Rt ...(2)
V = 0.4 # 12 = 4.8 Volt. 2
H2 = 9I Rt
105. (a) Explain how does a cell maintain current in a In later case, heat generated is 9 times the initial heat
circuit. generated.
(b) In the circuit given below the resistance of the c. If another conductor of 2R is connected in series
path xTy = 2 W and that of xZy = 6 W then total resistance = R + 2R = 3R .
(i) Find the equivalent resistance between x and Now heat generated H = I2 ^3Rh t
y.
H = 3I2 Rt
(ii) Find the current in the main circuit.
In this case, heat generated is three times.
(iii) Calculate the current that flows through the
path xTy and xZy. 107. (a) Derive an expression to find the equivalent
resistance of three resistors connected in series.
 Also, draw the schematic diagram of the circuit.
(b) Find the equivalent resistance of the following
circuit:

c. (i) Symbol is of variable resistor and it is used to

regulate the current.
(ii) Plug key is closed. When plug key is closed
Ans : [CBSE 2013]
current flows through the circuit.

109. Define resistance of a conductor. State the factors on

a. which resistance of a conductor depends. Name the
device which is often used to change the resistance
without changing the voltage source in an electric
circuit.
If the equivalent resistance is RS Calculate the resistance of 50 m length of wire of
then, V = IRS cross-sectional area 0.01 square mm and of resistivity
5 # 10-8 Wm .
But, V = V1 + V2 + V3
Ans : [CASE 20131
RS = R1 + R2 + R3
Resistance is the opposition offered in the path of flow
of current by the atoms or molecules of a conductor.
Factors affecting resistances:
a. length R ? l
b. area of cross-section R ? 1
A
c. nature of material.
b.
Rheostat is used to change the current in the
circuit without changing the voltage source.
Given: l = 50 m
1 = 1 + 1 + 1 A = 0.01 mm2 = 0.01 # 10-6 m2
Rp R1 R2 R3
r = 5 # 10-8 Wm
= 1 + 1 + 1 = 5+3+2 As R = r l = 5 # 10-8 # 50
6 10 15 30 A 0.01 # 10-6
= 10 R = 250 W
30
Rp = 3 W 110. (a) Calculate the resistance of the wire using graph.

108. (a) Name and state the law that gives relationship
between the current through a conductor and the
potential difference across its two terminals. Also,
express this law mathematically.
(b) Draw the V-I graph for this law. Justify your
answer.
(c) Write the name and use of the circuit components
whose symbols are given below.

(i) (ii)
(b) How many 176 W resistors in parallel are required
Ans : [CBSE 2013] to carry 5 A on a 220 V line?
a. The law is Ohm’s law. (c) Define electric power, Derive relation between
If the physical conditions of a conductor is kept power, potential difference and resistance.
constant then current through it is directly Ans : [CBSE 2012]
proportional to the potential difference applied
across it. a. R = TV = 2 - 0 W
TI 0.1 - 0
V ? I or V = RI
b. Since V ? I so a graph b/w V and I is a straight R = 20 W
line.
 1 = 1 + 1 + 1
R R1 R2 R3
b. To prevent oxidising the filament due to high
temperature.
c. The current in the fuse wire must not exceed 5 A
otherwise it will melt.

112. (a) In the circuit shown connect a nichrome wire of

length “L” between points X and Y and note the
ammeter reading.
b. Resistance of the circuit to carry a current of 5A (i) When this experiment is repeated by inserting
on 220V. another nichrome wire of the same thickness
but twice the length (2L), what changes are
R = 220 = 44 W observed in the ammeter reading?
5
Let n resistors of 176 W are connected whose (ii) State the changes that are observed in the
equivalent resistance is 44 W . ammeter reading if we double the area of
cross-section without changing the length in
176 = 44 or n = 176
n 44 the above experiment. Justify your answer in
both the cases.
n =4 (b) “Potential difference between points A and B in
a. The rate of electrical energy is consumed in a an electric field is 1V”. Explain the statement.
circuit is called electric power
2
P = W = I Rt
t t

P = I2 R But I = V
R
2 2
P = V 2 R or P = V Ans : [CBSE 2012]
R R
a. (i) The resistance of two times long wire also
111. (a) Three resistors R1, R2 and R3 are connected in becomes two times so current decreases in the
parallel and the combination is connected to circuit.
battery, ammeter, voltmeter and key. Draw (ii) If area of the nichrome wire is doubled then
suitable circuit diagram. Obtain an expression its resistance decreases and hence current
for the effective resistance of the combination of increases in the circuit.
resistors in parallel. b. Potential difference b/w A and B is 1 volt means
(b) Why are electric bulbs filled with chemically that 1 J of work is to be done in moving a unit
inactive nitrogen or argon? positive charge (+ 1C) from point A to B.
(c) What is meant by the statement that the rating of
a fuse in a circuit is 5 A? 113. Draw a circuit diagram for a circuit consisting of a
Ans : [CBSE 2012] battery of five cells of 2 volts each, a 5 W resistor, a
10 W resistor and a 15 W resistor, an ammeter and
a. Let equivalent (effective) resistance is R
a plug key; all connected in series. Also, connect a
then I =V voltmeter to record the potential difference across the
R
15 W resistor and calculate:
a. the electric current passing through the above
circuit and
b. potential difference across 5 W resistor when the
key is closed.
Ans : [CBSE 2012]

Similarly, I1 = V
R1

I2 = V and I3 = V a. Net effective resistance of the circuit.

R2 R3
R ^5 + 10 + 15h W = 30 W
But I = I1 + I2 + I3 Current in the circuit
V =V +V +V
or
R R1 R2 R3 I = ne = 5 # 2 A = 1 A
R 30 3
I = 0.33 A
 b. P.D. across 5 W resistor V = IR If by applying a potential difference of 1 volt across a
V = 0.33 # 5 = 1.65 Volt. conductor, the current is 1A then the resistance of the
conductor is said to be 1 ohm.
V = 1.65 Volt. Two disadvantages of connecting electrical appliance
in series.
114. (a) What is an electric circuit?
a. If one appliance fails to operate then the circuit
(b) Calculate the number of electron that flow per
is broken and other devices also will not operate.
second to constitute a current of one ampere.
Charge on an electron is 1.6 # 10-19 C . b. Different devices require different amount of
(c) Draw an electric circuit for studying Ohm’s law. current to operate but in series combination, same
current is supplied to all electrical appliances.
Label the circuit component used to measure
electric current and potential difference. 117. Define power. State the difference between 1 watt and
Ans : [CBSE 2012] 1 watt hour. Establish the relationship between unit
a. A continuous path in which current can flow when of electric energy and SI unit of energy. An electric
switch i6 plugged in. heater rated 1000 W/220 V operates 2 hours daily.
Calculate the cost of energy to operate for 30 days at
b. Q = It or ne = It & n = I $ t
e the rate of Rs 5.00 per kWh.
Given: I = 1A , t = 1s Ans : [CBSE 2012]
n = 1 # 1 -19 Electric Power: P is defined as the rate at which
1.6 # 10 electric energy is consumed in an electric circuit.
n = 6.25 # 1018 electrons 1 watt is the power consumed by an electric appliance
c. K–Plug key, (A)–Ammeter, (V)–Voltmeter, Rh– that carries 1A current when a potential difference of
Rheostat 1 volt is applied across it. Whereas 1 Wh. is the unit
of electric energy, which is consumed by an electric
appliance of 1 W power in one hour.
Commercial unit of electric energy is kWh.
1 kWh = 1000 W # 60 # 60 s
1 kWh = 3.6 # 106 J
Energy consumed by heater in one month
= 1000 W # 2h # 30 days = 60 kWh
115. (a) Define potential difference between two points in
= 60 units
a conductor.
Total cost @ ` 5/-kWh = 5 # 60 = `300
(b) Name the instrument used to measure the potential
difference in a circuit. How is it connected? 118. (a) Why is the series arrangement not used for
(c) A current of 2 A passes through a circuit for domestic circuits?
1 minute. If potential difference between the (b) Why is the tungsten used almost exclusively for
terminals of the circuit is 3 V, what is the work filament of electric lamps?
done in transferring the charges? (c) Why are the conductors of electric heating devices
Ans : [CBSE 2012] such as bread toasters and electric irons made of
a. Electric potential is the amount of work done in an alloy rather than a pure metal?
bringing a unit positive charge from one point to (d) Why are copper and aluminium wires usually
another. employed for electricity transmission?
b. Voltmeter. It is connected in parallel in the circuit. (e) Why does the cord of an electric heater not glow
c. I = 2A , t = 1 min. = 60 s , V = 3 V while the heating element does?
Ans : [CBSE 2010]
W = VQ = V ^It h
W = 3 # 2 # 60 J a. In the series arrangement if any device fails to
work, circuit will be broken and other devices stop
W = 360 J working. In series combination current remains
same. Where as different devices requires different
116. State Ohm’s law. Write the mathematical
current.
representation of Ohm’s law. Use this relationship to
b. Tungsten is used due to its high resistivity and
define 1 ohm. List two disadvantages of connecting
high melting point.
different electrical appliances in series.
c. Alloys have higher resistivity than their pure
Ans : [CBSE 2012] constituent and hence produces more heat.
If the physical conditions of a conductor are kept d. Copper and aluminium are good conductors and
constant then current is directly proportional to the have low values of resistivity so these are used for
potential difference applied across it. electric transmission.
Mathematical representation of Ohm’s law V = IR . e. Cords core made up of good conductor with low
V =R resistivity where as heating elements are made
I up of alloys of higher resistivity to produce more
heat.
1 Volt = 1 ohm
1 Ampere
119. (a) Name an instrument that measures electric 120. (a) (i) What is meant by saying that the potential
current in a circuit. Define the unit of electric difference between two points is 1 volt?
current. (ii) How much energy is given to 5 coulomb of
(b) What do the following symbols mean in circuit charge passing through a 12 V battery?
diagrams? (b) Describe an activity with necessary electric circuit
drawn to study the factors on which the resistance
(i) (ii) of a conducting wire depends.
(c) An electric circuit consisting of a 0.5 m long Ans : [CBSE 2008]
nichrome wire XY, an ammeter, a voltmeter, four a. (i) Potential difference b/w the two points is 1
cells of 1.5 V each and a plug key was set up. volt mean if we bring a unit positive charge (+
(i) Draw a diagram of this electric circuit to study 1C) from one point to other point then amount of
the relation between the potential difference work done is 1 J, W = VQ.
maintained between the points X and Y and (ii) Given: Q =5 C, V =12 V, W =12 # 5 = 60 J
the electric current flowing through XY. b. Activity to study the factors of affecting
(ii) Following graph was plotted between V and I resistance of the conductor—Take a cell, an
values: ammeter, manganin wires of different length and
different area of cross- section and key. Connect
an ammeter, a manganin wire of (say) 10 cm long
to a cell through a plug key.
(i). Now closed the key and note the current in
the circuit with the help of ammeter.
(ii). Now replace the manganin wire with another
manganin wire of twice the area of cross-
section and again measure the current in the
circuit with the help of ammeter.
(iii).Now repeat the activity by taking a copper
What would be the values of V/I ratios when the wire of same length same area of cross-section,
potential difference is 0.8 V, 1.2 V and 1.6 V and note down the current in each case. You
respectively? What conclusion do you draw from these will find that current in the circuit in each
values? case is different. Which shows that resistance
depends upon (1) nature of material (2)
Ans : [Delhi 2008]
length of the conductor and (3) area of cross-
a. Ammeter: Ampere is the unit of current. If one section.
coulomb charge flows in a circuit in 1 s then the
current in the circuit will be 1 Ampere. (A)
b. (i) Variable resistor (ii) closed key

c. (i)

121. (a) What do the following symbols represent in a

circuit? Write the name and one function of each.

(i) (ii)

(b) Draw a schematic diagram of a circuit consisting

of a battery of 12 V, three resistors of 5 W , 10
W and 20 W connected in parallel, an ammeter
to measure the total current through the circuit,
a voltmeter to measure the potential difference
(ii) across the combination of resistors.
(c) State any one advantage of connecting electrical
devices in parallel with the mains instead of
connecting them in series in a household circuit.
Ans : [CBSE 2008]
a. (i) Variable resistor used to change the current in
circuit.
(ii) Wires crossing each other which are not
The graph b/w V and I is a straight line. connected together. It is used when large
number of connections are to be made with
R = V = 1.6 - 0 = 1.6 = 2.67 W
I 0.6 - 0 0.6 the help of wires out joining them.
 Given: V = 1.5 volt.
R = 30 W
I = V = 1.5 = 1 = 0.05 A
R 30 20
b.
125. When two resistors of resistances R1 and R2 are
connected in parallel, the net resistance is 3 W . When
connected in series, its value is 16 W . Calculate the
values of R1 and R2.
Ans : [All India 2016]
c. (i) Let the devices are connected in series if one
devices fails to work, the circuit will be broken and R1 and R2 are in parallel combination.
all devices stop working, which is not in the case 1 = 1 + 1
of parallel combination. In parallel combination if Rp R1 R2
one device fails others keep working. R1 # R2 = 3
(ii) In parallel combination the voltage will be ...(1)
R1 + R2
same across each device. When R1 and R2 are in series combination.
122. An electric iron has a rating of 750 W; 200 V. Rs = R1 + R2 = 16 W
Calculate: R1 + R2 = 16 ...(2)
a. the current required. Solving eq. (1) and eq. (2)
b. the resistance of its heating element,
c. energy consumed by the iron in 2 hours. R 12 - 16R1 + 48 = 0
Ans : [CBSE2016] ^R1 - 4h^R1 - 12h = 0
Rating of iron is 750 W–200V. R1 = 4 W, 12 W
P = 750 W , V = 200 Volt. R2 = 12 W or 4 W

a. P = VI or I = P 126. A current of 0.5 A is drawn by a filament of an electric

V bulb for 10 minutes. Find the amount of electric charge
I = 750 = 3.75 A that flows through the circuit.
200
Ans : [CBSE 2015]
b. Resistance = V = 200 = 53.3 Volt.
I 3.75
Given: I = 0.5 A
c. Energy consumed in 2 hr = P # t
t = 10 # 60 s
E = 750 # 2 Wh = 1500 Wh
Q
I = or Q = It
123. A piece of wire is redrawn, without change in volume so t
that its radius is halved. Compare the new resistance Q = 0.5 # 10 # 60 C
with the original resistance. Q = 300 C
Ans : [CBSE2016]
127. (a) How much current will an electric bulb draw
Let l1 = l from a 220 V source, if the resistance of the bulb
2 2 filament is 1200 ohm?
A1 = pr = pr
1
(b) How much current will an electric heater coil draw
New length = l2 from a 220 V source, if the resistance of the heater
22 coil is 100 ohm?
A2 = p d r n = pr
2 4 Ans : [CBSE 2015]
Given: Volume is same
(a) Given:V = 220 V
l1 A1 = l2 A2
2
R = 1200 ohm
l # pr2 = l2 pr or l2 = 4l As V = IR
4

R1 = r l 2 and 220 = I # 1200 or I = 220 A

1200
^pr h I = 0.18 A
R2 = r 4l 2 = 16r l 2 (b) V = 220 V
pr pr
4 R = 100 ohm
R2 = 16R1
I = V = 220 A
R 100
124. The potential difference across the terminals of a I = 2.2 A
cell is 1.5 volt. If it is connected with a resistance of
30 ohms, calculate the current flowing through the 128. The potential difference between the terminals of an
circuit. electric heater is 60 V when it draws a current of 4 A
Ans : [CBSE2016] from the source. What current will the heater draw, if
 the potential difference is increased to 120 V? As P = V#I
Ans : a. When heating is at maximum rate
P = 840 W
V = 60 V , I = 4A
I = 840 = 3.8 A
R = V = 60 = 15 W 220
I 4
when V = 120 V , R = 15 W and R = V = 220 = 57.7 W
I 3.8
then, Il = V = 120 b. When heating is at minimum rate
R 15
P = 360 W
Il = 8A
I = 360 = 1.64 A
220
129. Resistance of a metal wire of length 1 m is 26 W at
20°C. If the diameter of the wire is 0.3 mm, what will and, Resistance = 220 = 1.34.15 W
be the resistivity of the metal at that temperature? 1.64
Ans : 132. In a household, 5 tube lights of 40 W each are used
for 5 hours and an electric press of 500 W for 4 hour
We have l = 1m everyday. Calculate the total energy consumed by the
R = 26 ohm tube lights and press in a month of 30 days.
Ans : [CBSE 2013]
t = 20cC
r = 0.15 mm Power of 1 tube = 40 W
r =? Power of 5 tubes = 5 # 40 W = 200 W
Energy consumed by 5 tubes in 5 hr. per day
As R =rl
A = 200 # 5 = 1000 Wh
2
r = R # A = R # pr Energy consumed by electric press per day
l l
= 500 W # 4 hr
^0.15 # 10-3h2
r = 26 # 22 # = 2000 Wh
7 1
Total energy consumed per day
r = 1.84 # 10-6 Wm
= ^1000 + 2000h Wh
130. A 4 W resistance wire is doubled on itself. Calculate = 3000 Wh = 3 kWh
the new resistance of the wire. Total energy consumed in 30 days
Ans : [CBSE 2015] = 3 # 30 kWh
Let the initial length = l = 90 kWh
Initial resistance = 4 W 133. In the circuit shown below, calculate:
when it is doubled on itself, length becomes half and a. total resistance in arm CE,
area becomes double (=2A) b. total current drawn from the battery, and
R1 = r l1 ...(1) c. current in each arm, i.e., AB and CE of the circuit.
A1

4 =rl
A

R2 = r l2 ...(2)
A2
l
R2 = r 2
2A

R2 = r l ...(3) Ans : [CBSE 2013]

4A
Dividing (3) by eq. (1) a. Total resistance in arm CE
R2 = r l A1 = l A = ^2 + 4h W = 6 W
R1 4A # rl1 4A # l b. CE arm and AB arm in parallel.
R2 = R1 = 4 = 1 effective resistance, b6 6l
1 = 1+1
4 4 R
R2 = 1 W R = 3W
131. An electric iron consumes energy at a rate of 840 W Total current in the circuit 6a V = 3V given@
when heating is at the maximum rate and 360 W when
the heating is at the minimum. The voltage is 220 V. I = V = 3 = 1A
R 3
What are the current and the resistance in each case? c. Resistance of CE and AB arms is same = 6 W
Ans : [CBSE 2015]
Current in each arm = 3 = 1 A
6 2
 the circuit, and (b) current shown by the ammeter.
I = 0. 5 A

134. An electric heater rated 1200 W operates 2 hour per

day. Find the cost of the energy required to operate it
for 30 days at Rs 5.00 per unit.
Ans : [CBSE 2013]

Rating of heater = 1200 W

t1 = 2 hr per day
Total time ^ t h for 30 days Ans : [CBSE 2012]
= t1 # 30 = 2 # 30 a. 3 W and 2 W resistors are in series their effective
resistance 3 + 2 = 5 W is in parallel to 5 W
= 60 hrs
resistance.
Energy consumed in one month (30 days)
= P # t = 1200 # 60 Net resistance = 5 = 2.5 W
2
= 72000 Wh
b. I = V = 2.5
= 72 kWh R 2.5
Cost of energy consumed in 30 days I = 1A
= `72 # 5 = `360
138. An electric heater rated 600 W operates 6 hours per
135. Two electric lamps of 100 W and 25 W respectively day. Find the cost to operate it for 30 days at Rs. 3.00
are joined in parallel to a supply of 200 V. Calculate per unit.
the total current flowing through the circuit. Ans : [CBSE 2012]
Ans : [CBSE 2012]
Given: P = 600 W
Bulbs 100 W 25 W
t = 6 hr per day
V = 200 V 200 V
no. of days = 30
Total P = P1 + P2 Energy consumed by the heater
= 100 + 25 = 125 W = P#t
I = P = 125 A = 600 W # 6 hr # 30 days
V 200 day
= 108000 Wh
I = 0.625 A
= 108 kWh
136. Two identical resistors, each of resistance 2 W are
Total cost @ ` 3/- = `108 # 3 = `324
connected in turn: (i) in series, and (ii) in parallel
to a battery of 12 V. Calculate the ratio of power 139. Three resistors of 5 W, 10 W, and 15 W are connected
consumed in the two cases. in series and the combination is connected to battery
Ans : [CBSE 2015] of 30 V. Ammeter and voltmeter are connected in
the circuit. Draw a circuit diagram to connect all the
Given: R1 = R2 = 2 W devices in proper correct order. What is the current
(i) In series RS = 2 + 2 = 4 W flowing and potential difference across 10 W resistance?
Power consumed in series: Ans : [CBSE 2012]
2
Effective resistance of the circuit
PS = V = 12 # 12 W
RS 4 R = 5 + 10 + 15 = 30 W
PS = 36 W
(ii) In parallel combination 1 = 1 + 1
Rp 2 2
RP = 1 W
2
PP = V = 12 # 12 W
RP 1
PP = 144 W

137. In the given circuit, calculate (a) total resistance of

Current in the circuit, I = V = 30 A
R 30
I = 1A
Current in 10 W resistor = 1 A
Potential difference across 10 W resistor
V = IR = 1 # 10
V = 10 Volt
140. Find the equivalent resistance across the two ends A resistance of coils
and B of this circuit. = 30 + 30 = 60 W
I = 220 = 3.66 A
60
c. When two coils are connected in parallel then
total resistance
= 30 = 15 A
2

Now current, I = 220 = 14.67 A

15
142. A piece of wire having resistance R is cut into four
equal parts,
Ans : a. How will the resistance of each part compare with
The pairs of Rl and R2; R3 and R4 ; R5 and R6 and R7, the original resistance?
and R8 are in parallel b. If the four parts are placed in parallel, how will
Their equivalent resistance = 1 W each. the joint resistance compare with the resistance of
the original wire?
Ans :
a. When wire is cut in equal pieces then resistance
on one piece = R4
b. Effective resistance in parallel combination of
these four pieces of resistance R4 each.
1 = 4 + 4 + 4 + 4 = 16
Rp R R R R R

Rp = R
16
Now R12 and R34 are in series R14 = 1 + 1 = 2 W and
R56 and R78 are in series 143. A wire is 1.0 m long, 0.2 mm in diameter and has
a resistance of 10 W . Calculate the resistivity of its
R56 = 1 + 1 = 2 W
material.
Ans : [CBSE 2011]

L = 1.0 m
D = 0.2 mm
r = D = 0.2 = 0.1 mm
2 2

Hence network can be reduced further as r = 0.1 # 10-3 m

R = 10 W
R = r l or r = R # A
A r
2
r = 10 # pr
l
Now R14 and R58 are in parallel
Net equivalent resistance of the network 3.14 # ^0.1 # 10-3h2
10 =
1.0
= 1 + 1 = 1W
2 2 r = 3.14 # 10-7 Wm
141. A hot plate of an electric oven, connected to a 220 V 144. The rating of an electric heater is 1100 W, 220 V.
line. It has two resistance coils A and B each of the Calculate its resistance when it operates at 220 V.
30 W which may be used separately, in series or in Also, calculate the energy consumed in kWh in the
parallel. Find the value of the current required in each month of November, if the heater is used daily for four
of the three cases. hours at the rated voltage.
Ans : [CBSE 2012] Ans : [CBSE 2010]
V = 220 Volt P = 1100 W
RA = RB = 30 W V = 220 V
a. When both are used separately. 2
Then current drawn by each R = V = 220 # 220 W = 484 W = 44 W
P 1100 11
I = V = 220 = 7.3 A Total energy consumed in the month of Nov. (i.e. 30
R 30 days) @ 4 hr per day.
b. When two coils are connected in series then total
 E = P#t I1 = I2 = 1.5 A
= 1100 # 4 # hr # 30 147. Find out the following in the electric circuit given in
= 1100 # 120 Wh figure:
E = 132 kWh a. Effective resistance of two 8 W resistors in the
combination.
145. (a) For the circuit shown in the diagram, calculate: b. Current flowing through 4 W resistor.
(i) value of current through the 30 W resistor. c. Potential difference across 4 W resistor.
(ii) total resistance of the circuit. d. Power dissipated in 4 W resistor.
(b) Give two advantages of connecting electrical e. Difference in ammeter readings, if any.
devices in parallel with battery.

Ans : [CBSE 2010] Ans :

a. Potential across each resistor = 6 V. a. 8 W and 8 W resistors are in parallel
(i) I in 30 W resistor, Rp = 8 # 8 = 4 W
8+8
=V = 6 = 1 A
R 30 5
= 0.2 A
(ii) All in parallel,
1 = 1 + 1 +1 = 1+3+6
Rp 30 10 5 30

= 10
30
Rp = 3 W b. Total resistance of the circuit
b. (i) Voltage across each appliance remains = ^4 + 4h W = 8 W
(ii) If any appliance fails to work other appliances Current in 4 W resistor
continue to work.
I = 8 = 1A
8
146. Three 2 W resistors, A, B and C, are connected as c. Potential difference across 4 W resistor
shown in figure. Each of them dissipates energy and V = IR = 1 # 4 = 4 Volt.
can withstand a maximum power of 18 W without d. Power dissipated in 4 W resistor
melting. Find the maximum current that can flow
P = I2 R = ^1 h2 # 4 W
through the three resistors.
P =4W
e. Both the ammeters are in series in the circuit so
current will be same in both ammeters. Hence no
difference in the reading of two ammeter.

148. Calculate the resistance of an electric bulb which

Ans : [CBSE 2010] allows a 10 A current when connected to a 220 V
power source.
Given maximum power of the network
Ans : [CBSE 2009]
P = 18 W
Maximum current in 2 W resistor. I = 10 A

from P = I R or I = P
2 2 V = 220 Volt.
R
I2 = 18 = 9 Resistance of bulb = V = 220 = 22 W
2 I 10

I = 3A 149. An electric lamp is marked 100 W, 220 V. It is used

for 5 hours daily. Calculate: (i) its resistance while
glowing, (ii) energy consumed in kWh per day.
Ans : [CBSE 2007]
Electric Iron 100W –– 220 V
Resistor 2 W, 2 W are equal and in parallel combination Used for time, t = 5 hr. daily
so current of 3 A will be distributed equally.
 2
= P # t = 100 # 4 = 400 Wh
(i) R = V = 220 # 220 = 484 W
P 100
= 0.4 kWh
(ii) Energy consumed by iron per day Total energy consumed by 5 similar bulb
= P # t = 100 # 5 Wh = 5 # 0.4 = 2 kWh
= 500 Wh = 0.5 kWh Cost ` 0.50 per unit = `2 # 0.50 = `1
150. A torch bulb is rated 5 V and 500 mA. Calculate
its (i) power (ii) resistance and (iii) energy consumed
when it is lighted for 4 hours.
Ans : [CBSE 2005]
Given: 5V––500 mA
(i) Power = V # I = 5 # 500 # 10-3
= 2.5 W
(ii) Resistance = V = 5 = 10 W
I 500 # 10-3
(iii) Energy consumed in four hrs.
= 2.5 # 4 # 60 # 60
= 10 # 3600 W.s.
= 3.6 # 10 4 J

151. If a 12 V battery is connected to the arrangement of

resistances given below, calculate:
a. the total effective resistance of the arrangement
and
b. the total current flowing in the circuit.

Ans : [CBSE 2005]

a. 10 W and 20 W are in series
Rs1 = 10 + 20 = 30 W
5 W and 25 W are in series
Rs2 = 5 + 25 = 30 W
30 W and 30 W are in parallel.
1 = 1 + 1 = 2
Rp 30 30 30
R p = 15 W
(ii) I = V = 12 = 0.8 A
RP 15

152. An electric bulb is rated at 200 V–100 W. What is its

resistance? Five such bulbs bum for 4 hours. What is
the electrical energy consumed? Calculate the cost, if
the rate is 50 paise unit.
Ans :

V = 200 V
P = 100 W
2
(a) P =V
R
^200h2
R = W = 40000 = 400 W
100 100
(b) Energy consumed in 4 hrs. by one bulb.
Chap 9 : Herededit and Evolution www.cbse.online

CHAPTER 9
Herededit and Evolution

ONE MARK QUESTIONS in next progeny?

Ans : [CBSE 2015]
Since no biochemical reaction is reliable, therefore, in
1. A Mendelian experiment consisted of breeding pea copying of DNA, it may cause slight difference which
plants bearing violet flowers with pea plants bearing causes these variations.
white flowers. What will be the result in Fj progeny?
Ans : [All India 2018]
All will bear violet flowers.

2. In a beetle population, the number of green beetles is

more than blue and red beetles. Give a reason behind
this situation.
Ans : [CBSE 2018]
Variation/Natural selection.

3. What indication do we get by reappearance of dwarf

plant in F2 generation?
Ans :
After obtaining progeny in F2 generation in a
dihybrid cross, Mendel concluded that when two 9. How can the chromosomes be identified?
pairs of traits are combined in a hybrid, one pair of
Ans : [CBSE 2015]
character segregates independently of the other pair
of character. In human beings, the individual chromosomes are
identified by their lengths, position of centromere and
4. How many pairs of chromosomes are present in human banding pattern on staining.
beings?
Ans : [CBSE 2016] 10. A normal baby girl receives her X chromosome from
whom : mother, father, both mother and father or
23 pairs. either from mother or father?
5. An organism which is a worm, has very simple ‘eyes’, Ans : [CBSE 2015]
that are really eye spots which detect light. Name that From both mother and father.
organism.
Ans : [CBSE 2016]
Planaria.

6. Why is the progeny always tall when a tall pea plant

is crossed with a short pea plant?
11. No two individuals are absolutely alike in a population.
Ans : [CBSE 2016]
Why?
The trait which represents the tallness in a pea plant Ans : [CBSE 2015]
is dominant over the another trait, shortness (dwarf).
All individuals have different kind of DNA. So all
7. All the variations in a species do not have equal individuals are not alike to each other.
chances of survival. Why?
12. When does the process of gene flow take place?
Ans : [CBSE 2015]
Ans : [CBSE 2015]
Some variations are caused by environmental changes
and they do not bring out any change in DNA. Gene flow or gene migration takes place in between
Therefore, all the variations do not have equal chances the populations that are partly but not completely
of survival. separated.

13. How are characters or traits controlled?

8. Why is it that asexual reproduction produces exact
copies but sometimes minor variations are also seen Ans : [All India 2014]
 Characters or traits of an organism are controlled by 24. Name the plant on which Mendel performed his
the genes /DNA. experiments.
Ans : [CBSE 2013,14]
14. What is a gene?
Ans : [All India 2014] Garden pea (Pisum sativum).

It is a functional piece of DNA that is responsible for 25. What are the basic events in evolution?
expression of a trait in the organisms. Ans : [CBSE 2013.14]
15. What is heredity? The changes in DNA during reproduction are the
Ans : [All India 2014] basic events in evolution.

Transmission of characters and traits from one 26. What is genetic drift?
generation to the next. Ans : [CBSE 2012,13]
16. Mendel observed a contrasting trait in relation to The change in the frequency of certain genes in a
position of flowers. Mention the trait. population over generations.
Ans : [All India 2014-15] 27. What are fossils?
Axial flower position (dominant), terminal flower Ans : [CBSE 2012, 13]
position (recessive).
Preserved traces of living organisms.
17. Name the term used for the traits that are exhibited
28. What are analogous organs?
externally.
Ans : [CBSE 2011, 12, 13]
Ans : [CBSE 2014]
The organs which have similar functions but different
Phenotype.
structures are called analogous organs.
18. Give the respective scientific terms used for studying:
29. The human hand, cat paw and the horse foot, when
a. the mechanism by which variations are created
studied in detail show the same structure of bones and
and inherited, and
point towards a common origin.
b. the development of new type of organisms from
a. What do you conclude from this?
the existing ones.
b. What is the term given to such structures?
Ans : [CBSE 2014]
Ans : [Sample Paper 2010]
a. Heredity
a. They have common origin/ancestory.
b. Species
b. Homologous organs.
19. Write the sex of the baby that inherits Y-chromosomes
30. When a tall and dwarf pea plant were crossed, Fx
from the father.
showed only tall plants but in F2 generation, some
Ans : [CBSE 2014] plants were dwarf. What does it mean?
Male. Ans : [CBSE 2008]
20. What is the phenotypic ratio of a dihybrid cross in F2 It means reappearance of the dwarf character, a
generation? recessive trait in B’2 generation shows that the dwarf
Ans : [CBSE 2014] trait/ character was present in individuals of F* but
it did not express (due to the present of tallness, a
9 : 3 : 3 : 1. dominant trait / character)
21. Give an example where sex determination is regulated 31. How is the age of fossil determined?
by environmental factors.
Ans : [Panchkula 2008]
Ans : [CBSE 2014]
The age of fossil fuels is determined through carbon-
In snail, sex is determined by environmental factors dating or time dating method.
(temperature).
32. What is evolution?
22. Define speciation.
Ans : [Panchkula 2008, CBSE 2013,14]
Ans : [CBSE 2013,14]
Gradual unfolding of organisms from pre-existing
Speciation means origin of new species from the organisms through change is called evolution.
existing one.

23. What is the effect of DNA copying which is not TWO MARKS QUESTIONS
perfectly accurate on the reproduction process?
Ans : [CBSE 2013,14]
33. What are fossils? What is their significance in the
It will result in less variations which may further lead study of evolution?
to less adaptation to changing environment, thus,
Ans : [Sample Paper 2016-17]
giving less chances of survival.
Fossils are impressions of the body/ body parts or
 the remains of organisms living in the past, which got or second generation.
preserved in sediments of earth.
a. Study of fossils helps in working out evolutionary 40. “The chromosome number of the sexually producing
relationships. parents and their offspring is the same”. Justify this
b. Fossils provide one of the most acceptable statement.
evidences in support of evolution, because we can Ans : [CBSE 2015]
study the evolutionary past of individuals in the In sexual reproduction, both the gametes (male and
form of their fossils. female) contain half the number of chromosomes
c. Age of fossils can also be found by time dating (haploid or n) and by the fusion of these gametes,
using isotopes of carbon! carbon dating. the zygote have full set (diploid 2n) chromosomes.
d. By studying fossils occurring in different strata of
rocks, geologists are able to reconstruct the time 41. If YYRR is round yellow, what do the following
course of evolutionary events. represent?
yyrr yyRR
34. (a) On what rules inheritance is based?
Ans : [CBSE 2015]
(b) Is each trait influenced by both paternal and
maternal DNA? yyrr - Wrinkled, green seeds
Ans : [CBSE 2016] yyRR — Round, green seeds

a. The rules of inheritance is based on the fact that 42. How did Mendel explain that it is possible that a trait
the traits in the progeny are carried out by DNA’s is inherited but not expressed in an organism?
of both the parents (mother and father). These Ans : [All India 2017]
rules are known s ‘Mendel’s Laws of Inheritance’.
The rules are: Yes, it is possible.
(i) Law of dominance, Example - When pure tall pea plants are crossed
(ii) Law of segregation, and with pure dwarf pea plants, only tall pea plants are
(iii) Law of independent assortment. obtained in F1 generation.
b. Yes, it is true that each trait is influenced by both On selfing tall plants of F1 both tall and dwarf
paternal and maternal DNA. plants are obtained in F2 generation in the ratio 3:1.

35. a. What is the genetic constitution of human sperm? Reappearance of the dwarf character, a recessive
b. Mention the chromosomes pair present in zygote trait in F2 generation shows that the dwarf trait/
determining the sex of a male child. character was present in individuals of F1 but it did
not express (due to the present of tallness, a dominant
Ans : [CBSE 2016]
trait / character)
a. 22 + Y or 22 + X
b. (22 + Y + 22 + X) 43. What is a dominant trait with respect to height in pea
plant. Give any two examples.
36. a. How many gene sets should a germ cell have? Ans : [All India 2014]
b. Mention two factors causing evolution.
Characters/Traits like ‘T’ are called dominant trait
Ans : [CBSE 2016]
(because it express itself) ‘t’ are recessive trait
a. One gene set. (because it remains supressed).
b. (i) Reproduction isolation (ii) Natural selection
Character Dominant Trait Recessive Trait
37. What is micro evolution? Does it explain speciation? Seed shape Round Wrinkled
Ans : [CBSE 2016] Pod shape Inflated Constricted
a. In micro evolution, the changes are small which
Pod colour Green Yellow
occurs in lower categories and change the common
characteristics of a particular species. Height of plant Tall Dwarf
b. It does not properly explain speciation.

38. In an area A, the leaf materials available to beetles

were very less. What are the two consequences seen in 44. Variations are important for the survival of species
case of beetles? overtime. Justify this statement with reasons.
Ans : [CBSE 2015] Ans : [CBSE 2014]
a. Due to poor nutrition, the average weight of adult a. It causes adaptations,
beetles decreases. b. It promotes natural selection.
b. The number of beetles (population) decreases due
45. How can we say that change in genes can be brought
to starvation.
about the change in DNA?
39. What is F2 generation? Ans : [CBSE 2014]
Ans : [CBSE 2015] A gene is a segment of DNA on a chromosome
The generation produced by the offsprings of F1 occupying a specific position.
generation i.e., first generation as parent is called F2 a. It provides informations from one protein to
 another and is responsible for its alteration. surface”. Comment on the statement stating
b. It ensures the stability of the DNA of the species. reason.
So, we can say that change in gene segment b. List two factors which could lead to the rise of
can bring about change in DNA. new species.
Ans : [CBSE 2013]
46. Where are the genes located? What is the chemical
a. This statement is correct as the fossils found
nature of gene?
closer to the surface of earth are more recent and
Ans : [CBSE 2014] those found in deeper layers are older ones.
Genes are located on chromosomes in linear sequence b. Natural selection and genetic drift.
and at fixed positions. Chemically, genes are acidic in
52. “Experience of an individual during its lifetime cannot
nature since they are nucleic acids which constitute
DNA. be passed on its progeny and cannot direct evolution”.
Justify this statement giving an example.
47. State the meaning of inherited traits and acquired Ans : [CBSE 2013]
traits. Which of the two is not passed on to the next
Since acquired characters are not inherited over
generation? Explain with the help of an example.
generations. Change in non-reproductive tissues
Ans : [All India 2013, (C) 2008] cannot be passed on to the DNA of the germ cells.
Acquired Trait Inherited Trait 53. What are sex chromosomes? Which sex chromosomes
1 Experiences of an Genetically inherited are found in male and female human beings? State the
individual during its chromosome responsible for the development of male
lifetime. child in human beings?
Ans : [CBSE 2013]
2. It cannot be passed on They can be passed on
from one generation to from one generation to Sex chromosomes are set of chromosomes present in
the next. the next. human beings which help in sex determination.
XX and XY.
3. Example: power to lift Example: Eye colour
Y chromosome.
weights and reading or height
French 54. How are fossil studies important in working out
evolutionary relationships. How would the age of
48. Tails of some mice were amputated and they were
fossils be determined?
allowed to breed. The mice that were produced also
had their tails amputated and it was repeated for Ans : [CBSE 2012]
many generations. What is the reason of tail appearing Fossils are impressions of the body/ body parts or
again and again? the remains of organisms living in the past, which got
Ans : [All India 2013] preserved in sediments of earth. Any remains of an
organism that has been preserved in the earth’s crust.
Such traits are acquired traits. Traits acquired during
Study of fossils helps in working out evolutionary
the life-time of an individual are not inherited as these
relationships. Age of fossils can be determined by time
changes are not in the genes of reproductive tissues.
dating using isotopes of carbon (carbon dating).
The changes in the non-reproductive tissues cannot be
passed on to the DNA of the germ cells, hence such 55. A tall pea plant was crossed with a dwarf one. F1
acquired changes are not inherited by the progeny. generation was allowed to self pollinate and F2
Example: tailless mice (if tail is removed by surgery) generation was also obtained. Answer the following
cannot produce tailless progeny. questions:
a. What would be the phenotype of plants in F1
49. a. Write full form of DNA.
generation?
b. Why are variations essential for the species?
b. What would be the phenotypic ratio in F2
Ans : [CBSE 2013] generation?
a. Deoxyribonucleic acid c. Give reason for your observation in F1 generation.
b. Survival Ans : [CBSE 2012]
50. What is the importance of DNA copying in a. all tall
reproduction? Why is variation beneficial to the b. 3:1
species but not necessary for the individual? Explain. c. Reason: The tall trait of pea plant is dominant
trait over short trait, a recessive trait.
Ans : [CBSE 2013]
DNA copying is essential part of reproduction because 56. A violet pea plant [VV] was crossed with a white
it ensures that same blueprint of the body design is one[vv]. F1 generation was allowed to self pollinate
maintained. Variation for the species is beneficial for and F2 generation was also obtained,
adaptation and better survival. It may result in new Answer the following questions:
species formation. a. What would be the phenotype of plants in F1
generation?
b. What would be the percentage of plants with
51. a. “Recent fossils are found closer to the earth’s
 white flowers in F2 generation? themselves to produce fertile offsprings.
c. What would be the ratio of vv: Vv in F2
generation. 60. Some of the traits are acquired while others are
inherited. Explain. Which of two will not be passed
Ans : [Delhi 2012]
on to next generation?
a. all violet flowers Ans : [Delhi 2009 C]
b. 25%
c. 1 : 2. Acquired traits are those features which are present
in an organism due to experiences during its life time,
57. a. Do eyes of octopus, insect and human show for example, swimming and knowledge of a language
relation in their evolutionary process? in human beings.
b. How can we say that birds have evolved from Inherited traits are those features which are
reptiles? transferred from one generation to the next through
Ans : [CBSE 2012] DNA or genes present in the cells of a reproductive
a. No, eyes of these animals do not show any tissue. For example, colour of eyes and hair in human
evolutionary relationship as they are analogous beings.
organs. Traits acquired during the life time of an individual
b. The presence of feathers both in dinosaurs and can not be inherited because the information of this
birds indicate birds have evolved from reptiles. feature is not ingrained in the DNA of individual.
Some organs may be adapted to perform new
functions during evolution, e.g., feathers which 61. What is the difference between homologous and
were meant for providing insulation in cold analogous organs? Give one example each.
weather, slowly became adapted for flight. Hence Ans : [CBSE 2008 C, 2012]
birds are closely related to reptile as dinosaurs
a. Homologous organs: Structures in animals share
had feathers, though could not fly.
a common ancestry. The structure, which has
58. From the set of figures given below, make a pair of similar basic structure and developmental origin
homologous and analogous organs each and give one but perform different functions.
reason in case of both, to justify your answer. For example: Fore limbs in vertebrates.
Homologous organs give an evidence of common
ancestory and evolutionary relationship between
apparently different species.
b. Analogous organs: Analogous organ are the
organs in different organisms which have different
basic structure but have similarity in shape and
function. However, these organs do not provide an
evidence in support with common ancestory, e.g.,
Wings of bat and bird.

THREE MARKS QUESTIONS

62. Discuss the role of variations in evolution. What is

Ans : [Sample Paper 2010] natural selection and genetic drift? [CBSE 2017]
Organs: or
a. Bird wing and Bat wing - Analogous organs. Explain the following:
Structures are different but functions are same. (a) Speciation (b) Natural Selection
b. Human forelimb and Bird wing — Homologous Ans : [All India 2015, CBSE 2011]
organs. a. The members of a population have minor
Structure are same but functions are different. differences among them which is called variations.
b. Two sources of variations are sexual reproduction
59. Why do human beings look different from each other?
and environmental factors.
What do you mean by species?
c. Sexual reproduction has greater chances of
Ans : [All India 2009] producing variation.
Human beings are sexually reproducing organisms. d. Variations with some advantage has greater
Genetic recombination occurs during gamete chances of surviving, for example, long neck of
formation in the sex organs followed by union of giraffe.
two gametes coming from two parents with different e. Natural selection and genetic drift lead to
genetic combination. Thus it ensures more diversity formation of new species hence evolution.
in characteristics in terms of colour, size, and looks. Natural Selection: Some variations may have
Inspite of this, they are able to reproduce among survival advantage hence they happen to gain
themselves to produce fertile offsprings. A species over others so that they can propagate more than
is a group of individuals which have some common others. Ultimately such variations are selected and
characters and they are able to reproduce among propagated among all members of the population.
 This is called adaptation of the species which with pure dwarf pea plants, only tall plants were
help them to cope well in their surroundings. obtained in F1 generation. On self pollinating the
In course of time, it could lead to accumulation F1 progeny, both tall and dwarf plants appeared
of adaptation. In geographically separated in F2 generation in the ratio 3 : 1.
populations of a species and development of Appearance of tall character in both the F1
reproductive barrier among them may lead to the and F2 shows that it is a dominant character.
formation of a new species. The absence of dwarf character in F1 generation
Genetic Drift: Some variation may not give and its reappearance in F2 shows dwarfness is the
survival advantage to members of population. recessive character.
But if by chance other variations are wiped out b. When Mendel conducted a dihybrid cross having
from populations, the remaining variations get two sets of characters, he obtained only one set of
propagated in next generations. parental characters in F1 generation whereas in F2
generation he obtained both the set of parental
63. Explain how gene expresses itself in a cell? Why are characters now recombined in the ratio of 9 : 3 :
we somewhat similar to our parents yet not identical 3 : 1.
to them? The appearance of new recombinants in the
Ans : [CBSE 2017] F2 generation along with parental type shows that
Genes are functional segments of DNA. They are units traits are inherited independently.
of heredity that gets passed on through reproduction
66. “Natural selection and speciation lead to evolution”.
from parents to progeny. It is the blue print of life.
Justify the statement.
DNA expresses itself through synthesis of proteins.
Proteins make structures in our body and also controls Ans : [Delhi 2017]
the functioning. In other words cells, tissues, organs Natural selection: Some variations are advantageous
and hence a living body expresses the traits inherited for an organism to adapt better in the prevailing
as genes/ DNA. Since we inherit the DNA, half from conditions of habitat. It makes it easy to obtain food
one and half from other parents, hence we somewhat and mating partner by them. In this manner they are
resemble them. At the same time we show mixed able to propagate more, transmitting their genes to
traits of both so can not be identical to either of them. next generation and producing more individuals with
similar genetic makeup and phenotype.
64. “It is a matter of chance whether a couple will have a. It leads to change in frequency of some genes in
a male or a female child.” Justify this statement by a population which give survival advantage to a
drawing a flow chart. species from elimination.
Ans : [Foreign 2015,2017] b. When most of the members of a population
Women produce only one type of ovum (carrying possess this variation, it is called its adaptation.
X chromosome) and males produce two types of c. Over a period of time large numbers of adaptations
sperms (carrying either X or Y chromosome) in equal are accumulated in the various populations of a
proportions. So the sex of a child is a matter of chance species which may be physically segregated from
depending upon the type of sperm fertilizing the ovum. each other.
d. Geographical barriers like mountains, rivers
etc., lead to incapability to reproduce amongst
themselves in the population.
e. By processes like genetic drift and natural selection
combined with geographical separation, when the
populations of a species become incompatible/
fail to reproduce with each other, speciation
- evolution of a new species from pre-existing
species - occurs.

67. With the help of one example each, distinguish between

inherited traits and acquired traits. Why are the traits
acquired during the life time of an individual not
inherited in the next generation? Explain the reason
of this fact with an example. [All India 2017]
or
Distinguish between inherited traits and acquired
traits in a tabular form, giving one example of each.
Ans : [Delhi 2017]

65. How do Mendel’s experiments show that the Acquired Trait Inherited Trait
a. traits may be dominant or recessive,
1 Experiences of an Genetically inherited
b. traits are inherited independently?
individual during its
Ans : [All India 2017] lifetime.
a. When Mendel cross pollinated pure tall pea plants
 Acquired Trait Inherited Trait b. Mendel studied that genes segregate during the
formation of gametes (sperms in males and ova in
2. It cannot be passed on They can be passed on females) and they again combine in the offspring
from one generation to from one generation to (one from each parent) and appear as dominant or
the next. the next. recessive trait. This can be worked out by making
3. Example: power to lift Example: Eye colour a test cross.
weights and reading or height c. Mendel proposed three laws, namely:
French (i) Law of segregation: Each inherited trait is
defined by a pair of gene. Parental genes are
68. What is evolution? How does it occur? randomly separated to the germ-cells so that
Ans : [All India 2016] germ contain only one pair of gene.
(ii) Law of independent assortment: Genes of
Organic Evolution: Gradual unfolding of organisms
different traits are sorted separately from one
from pre-existing organisms through change is called
another so that the inheritance of one trait is
evolution.
not dependent on the inheritance of another.
a. Evolution occurs in the form of genetic drift and
(iii) Law of dominance: An organism with alternate
natural selection combined with geographical
forms of a gene will express the form that is
separation.
document.
b. Speciation - evolution of a new species from pre-
existing species-occurs. 71. a. What function is performed by human arms,
c. Fossils are impressions of the body/body parts or forelimbs of dog and forelimbs of whales?
the remains of organisms living in the past, which b. Which type of organs are these?
got preserved in sediments of earth. c. Why do we call them so?
d. Study of not living species but also fossils helps in
Ans : [CBSE 2016]
working out evolutionary relationships.
e. Fossils provide one of the most acceptable a. Human arm : holding things Forelimbs of dog :
evidences in support of evolution, because we can running Forelimbs of whales : paddles
study the evolutionary past of individuals in the b. Homologous,
form of their fossils. c. Same origin, different functions.

69. “Two areas of study namely evolution and classification 72. If a population of red beetles, living on green bushes,
are interlinked”. Justify this statement. is being eaten by crows. During sexual reproduction,
Ans : [All India 2016,2017] a green beetle is found in progeny:
a. What is the future of new trait?
All living things are identified and categorised on the b. Will it survive in the new habitat?
basis of their body design in form and function. After a
Ans : [CBSE 2016]
certain body design comes into existence, it will shape
the effects of all other subsequent design changes a. Among progeny, when green beetle is found, it
simply because it already exists. So, characteristics escaped attack of crows as it merged with green
which came into existence earlier are likely to be colour. Green beetles increased, red decreased.
more basic than characteristics which have come into b. New trait will survive.
existence later.
73. An angiosperm plant having red coloured flowers
This means that the classification of life forms will when crossed with the other having the same colour
be closely related to their evolution. On connecting produced 40 progenies, out of which 30 plants were
this idea of evolution to classification, it is seen with red coloured flowers, 10 plants were with white
that some groups of organisms with ancient body coloured flowers. Find out:
designs have not changed very much. However, other a. What is the possible genotype of parent plants?
groups of organisms have acquired their particular b. Which trait is dominant and recessive?
body designs relatively recently. Because there is a c. What is this cross called as and what is its
possibility that complexity in design will increase over phenotypic ratio?
evolutionary time, it may not be wrong to say that Ans : [CBSE 2016]
older organisms are simpler, while younger organisms
are more complex. a. Rr and Rr.
b. Red colour of flowers is the dominant trait while
70. Explain Mendel’s concept of heredity, by giving three white colour is the recessive trait.
points. c. Monohybrid cross, phenotypic ratio is 3 : 1.
Ans : [CBSE 2016]
74. What is DNA copying? State its importance.
a. Mendel worked on pea plant {Pisum sativum) and Ans : [Delhi 2015]
discovered the fundamental laws of inheritance. He
found that traits (characteristics) are controlled A process where a DNA molecule produces two similar
by factors (which are now called genes) and each copies of itself in a reproducing cell.
factor (gene) come in pairs. These factors (genes) Importance -
are inherited as distinct units, one from each a. It makes possible the transmission of characters
parent. from parents to the next generation.
b. It causes variation in the population.
75. “We cannot pass on to our progeny the experiences denoted by ww.
and qualifications earned during our lifetime”. Justify a. What is the expected colour of the flowers in their
the statement giving reason and examples. F1 progeny?
Ans : [Delhi 2015] b. What will be the percentage of plants bearing
white flower in F2 generation, when the flowers of
Acquiring knowledge / skill in one’s lifetime such as
F1 plants were selfed?
learning dance, music, physical fitness or any other
c. State the expected ratio of the genotypes BB and
suitable example.
Bw in the F2 progeny.
Reason:
a. Such characters / experiences acquired during Ans : [CBSE 2015]
one’s lifetime do not bring any change in the DNA a. F1 generation — blue.
of the reproducing c$ll/germ cell. b. 25%
b. Only germ cells are responsible for passing on the c. BB : Bw = 1 : 2.
characters from the parents to the progeny.
80. Give reasons for the following:
76. a. Insects, octopus and vertebrates all have eyes. a. Traits acquired during lifetime of an individual
Can we group eyes of these animals together to are not inherited.
establish a common evolutionary origin? Justify b. All the human beings belong to a single species.
your answer. c. Variations keep on accumulating during
b. “Birds have evolved from reptiles”. State evidence reproduction and do not disappear in next
to prove the statement. generation.
Ans : [Delhi 2015] Ans : [CBBE 2015]
a. No, the structure of the eye in each of the a. These are acquired traits that do not make any
organisms is different. change to the DNA of an organism.
b. Fossils of certain dinosaurs/reptiles show imprints b. Homo sapiens originated in Africa and spread
of feathers along with their bones but they across the globe in stages. The humans with
could not fly presumably using the feathers for different colours in different regions have come
insulation. into being as an accident of evolution, so that
Later they developed / evolved and adapted they could live their lives the best they could. So
feathers for flight, thus becoming the ancestors of all belong to the same species.
present day birds. c. Inheritance from the previous generation provides
(OR any other suitable evidence/example) both a common basic body design, and subtle
changes in it, for the next generation. So the
77. What are chromosomes ? Explain how in sexually changes keep on accumulating generations after
reproducing organisms the number of chromosomes in generations.
the progeny is maintained.
Ans : [Outside Delhi 2015] 81. In a pea plant, find the contrasting trait if:
a. the position of flower is terminal.
Chromosomes - Thread like structures made up of
b. the flower is white in colour.
DNA found in the nucleus. The original number of
c. shape of pod is constricted.
chromosomes becomes half during gamete formation.
Hence, when the gametes combine, the original Ans : [CBSE 2015]
number of chromosomes gets restored in the progeny. a. Axial position of flower.
(or same thing explained in the form of a flow chart). b. Purple colour of flower.
c. Inflated shape.
78. Explain with an example for each, how the following
provides evidences in favour of evolution in organisms: 82. a. “Chromosomes are heredity carriers.” Why do we
a. Homologous organs say so?
b. Analogous organs b. Which vital function is not controlled by
c. Fossils autosomes?
Ans : [All India 2015, 2016, 2011, Delhi 2017] Ans : [CBSE 2015]
a. Homologous organs - study of homologous organs a. Chromosomes are made-up of DNA. Genes are
suggests that the organs having same structure located on the chromosomes. It is the DNA copy
but performing different functions have evolved which transfers from both the parents to their
from a common ancestor. Example: forelimbs of a offspring. Therefore, chromosomes made-up of
frog, lizard, bird and man. DNA and containing genes are said to be the
b. Analogous organs - show adoption of organs for heredity carriers.
common use. Example: wings of butterfly and b. Sex of the child is not controlled by autosomes.
wings of bat.
c. Fossils - provide the missing links between two 83. a. During evolution some changes may have occurred
species. Example: - Archeopteryx / fossils of some for a reason but proved to be useful for some other
dinosaurs with feathers. purpose. Cite one such example.
b. Has the evolutionary changes took place all of
79. A pea plant with blue colour flower denoted by BB sudden. Elaborate.
is cross-breed with a pea plant with white flower Ans : [All India 2014]
 a. Evolutions of feathers: Functional Advantage: A c. Birds developed feathers for insulation.
change that is useful for one property to start
with can become useful later for quite a different 86. With the help of suitable examples, explain why certain
function. Feathers, for example, can start out as traits cannot be passed on to the next generation.
providing insulation in cold weather. But later, What are such traits called?
they might become useful for flight. In fact, some Ans : [CBSE 2014]
dinosaurs had feathers, although they could not Example: Acquiring knowledge by reading/change
fly using the feathers. Birds seem to have later in body weight. Reason: Because such changes do
adapted the feathers to flight. This, means that not bring any change in the DNA of the germ cells/
birds are very closely related to reptiles, since such changes take place only in the non-reproductive
dinosaurs were reptiles. Birds have evolved from tissues.
reptile. Traits: Acquired traits.
b. Evolution changes has not took place all of
sudden. Evolution takes place in stages, i.e., bit 87. List three main factors responsible for the speciation
by bit over generations. Even an intermediate and briefly describe each one of them.
stage, such as a rudimentary eye, can be useful Ans : [CBSE 2014]
to some extent. This might be enough to give a
fitness advantage. In fact, the eye seems to be a Genetic Drift: Random change in the frequency of
very popular adaptation. genes.
Insects have them, so does an octopus, and Natural Selection: Nature selects the fittest individual
so do vertebrates. And the structure of the eye in in a population. Reproductive Isolation: When two
each of these organisms is different - enough for individuals are geographically isolated and natural
them to have separate evolutionary origins. selection operates upon them differently leading to
inability of the individuals to interbreed.
84. Variation is useful for the useful over long time. But
the variants have unequal chances of survival. Explain
this statement. [All India 2014-15]
or
Define variation in a species. How does it increases the
survival chances of a species?
a. Identify the organism shown in the above figure.
b. Name one incipient feature selected by the nature.
c. Mention any other primitive feature of birds.
Ans : [All India 2014-15]
Variation are minor differences among members
of a population. They are useful for the process of
evolution which take place over long time. But some of
the variants find it more advantageous in the present
environmental conditions to survive than others
88. (a) Which type of organs are shown in the figure
variants by virtue of the variation possessed by them
below?
hence they have unequal chances of survival. Thus
some get selected and others get eliminated. Those
which survive pass their genes to next generation
therefore frequency of genes possessed by them
increase in frequency in the population. Example - in
a population of beetles, a new variation (green colour)
get survival benefit/advantage to green beetles
whereas other (red) perishes.

85. (a) Identify the organism shown in the above figure. (b) Which type of origin and structure do these
organs have?
Ans : [CBSE 2014]
a. These are organs which help in flying (wings of
insects and wings of birds).
b. The structure and components of these wings are
different. They look similar because they have a
common use for flying, but their origins are not
common, i.e., they are analogous.
(b) Name one incipient feature selected by the nature.
(c) Mention any other primitive feature of birds. 89. (a) “Each organism has its own identity”. Explain.
Ans : [All India 2014-15] (b) What is speciation?
Ans : [CBSE 2014]
a. Planaria.
b. Eyes which were there only for detecting light. a. (i) The DNA of each organism is different from
 others. makeup and phenotype.
(ii) The DNA of each organism is specific within
the same species with specific number of 94. Rekha is very dark in colour. She stays very quiet at
chromosomes/genes. home and in her class also. She is always seeing for
b. Emergence of new species from pre-existing forms the beauty products which can help her to become
through natural selection/artificial selection/ fair. Her friend Lila talks to her about excessive use
genetic drift/evolution, etc. * of beauty products and tells her that they are very
harmful and colour comes by birth and she is not
90. An organ like a wing in birds are an advantage to an responsible for her dark colour.
organism. Did they appear in different stages or were a. What might have caused Rekha’s colour to be
formed due to a single sudden change in them. dark?
Ans : [CBSE 2014] b. Is it possible that all the family members of
Rekha’s family were dark?
Feathers in dinosaur were long and they could not
c. What value do you learn?
fly using feathers. It gave them protection from cold
weather and warmth. Birds seem to have later adapted Ans : [All India 2013]
the feathers to flight. a. Her dark colour may be due to the genetic
inheritance.
91. How are fossils formed? Describe, in brief, two methods b. All may not be dark, depending upon the genes
of determining the age of fossils. inherited and the environmental conditions that
Ans : [All India 2013] each one of them living in.
Fossils are formed when dead organisms are not c. Awareness, logical thinking, scientific
completely decomposed. The organisms may get temperament.
trapped in resins of tree, lava of volcanoes or hot mud
95. A cross was carried out between a pure bred tall pea
which when hardens, retains the animal’s parts thus,
plant and a pure bred dwarf pea plant and F1 progeny
forming fossils.
was obtained. Later, the F1 progeny was selfed to
Two methods of determining the age of fossils:
obtain F2 progeny. Answer the following questions:
a. Relative method: By estimating the age of the
a. What is the phenotype of the F1 progeny and
layer of earth’s crust where the fossil is found.
why?
Fossils near the surface are recent and those in the
b. Give the phenotypic ratio of the F2 progeny.
deeper layers are more ancient.
c. Why is the F2 progeny different from the F1
b. Radio-carbon dating method: By detecting the
progeny?”
ratios of different isotopes of carbon in the fossils.
Ans : [CBSE2013,14]
Fossils help in determining the connecting links
between various groups and their origin from their a. Tall, because genes responsible for tallness are
primitive ones, e.g., Archaeoptyrx. dominant over dwarf trait.
b.
92. Explain the term homologous organ with an example.
Ans : [All India 2013]
The organs which have similar basic structure and c. Because in F2 generation, recessive genes got
mode of origin but perform different functions in expressed in homozygous condition.
different animals are called homologous organs. E.g.,
Forelimbs of amphibians, reptiles, birds and mammals. 96. a. State any two factors that could lead to the rise of
Homologous organs give an evidence of common a new species.
ancestory and evolutionary relationship between b. How do analogous organs provide evidence in
apparently different species. favour of evolution?
Ans : [CBSE 2013]
93. How green beetles had colour advantage over red
beetles? Explain. a. Natural Selection, Genetic drift, Mutations,
Variations.
Ans : [All India 2013] b. The organs which are similar in function but are
Green beetle merge with green background of structurally different suggest that although these
vegetation which give survival advantage to a species two organs may look alike superficially giving
from elimination. an idea of common ancestory but the different
a. in the population of beetles, the new variation in structure and origin suggests that organisms
(green colour) get survival benefit / advantage to having these organs have a distant ancestor but
green beetles whereas other (red) perishes. such organs have developed during the course of
b. It is because of Natural selection — some variations evolution as an adaptation to similar mode of life.
are advantageous for an organism to adapt better
in the prevailing conditions of habitat. It makes it 97. a. Why traits such as intelligence and knowledge
easy to obtain food and mating partner by them. cannot be passed on to the next generation?
In this manner they are able to propagate more, b. How can we say that birds are closely related to
transmitting their genes to next generation and reptiles and have evolved from them?
producing more individuals with similar genetic Ans : [CBSE 2013]
 a. Traits such as intelligence and knowledge are observation regarding their ancestry?
not heritable traits, which do not bring upon Ans : [Delhi 2012]
any changes in the DNA of the germ cells and,
The organs which have similar basic structure and
therefore, cannot be passed on to the progeny.
mode of origin but perform different functions in
b. This can be said because traits such as feathers
different animals are called homologous organs, e.g.,
were first seen in reptiles like Dinosaurs, which
forelimbs of amphibians, reptiles, birds and mammals.
performed the function of providing insulation
Homologous organs give an evidence of common
to them in cold weather although they could not
ancestory and evolutionary relationship between
fly using the feathers but later birds adapted
apparently different species.
the feathers for flight. This means that birds are
very closely related to reptiles, as dinosaurs were Analogous organ are the organs in different
reptiles. organisms which have different basic structure but
have similarity in shape and function, e.g., wings of
98. (a) Differentiate between: bat and bird. These organs do not provide an evidence
1. Homologous organs and Analogous organs. in support with common ancestory.
2. Pollination and Fertilization
(b) What do fossils tell us about the process of
evolution? THREE MARKS QUESTIONS
Ans : [CBSE 2013]
a. (i) Organs in different organisms with same origin 102. A group of grasshoppers — some green and some
with different function/ different origin, same brown lived in a grassland having dry bushes and dry
function. grass.
(ii) Transfer of pollen from the stamen to the a. Which one would normally be picked up by
pistil of the flower/fusion of male and female predatory birds and why?
gametes. b. Population of which grasshopper will increase?
b. Help in establishing links and act as evidence of c. Name this phenomenon.
evolution. Ans : [Sample Paper 2010]
99. (a) Explain giving examples how artificial selection a. Green grass hopper, because they stand out,
has helped in the formation of newer varieties of against brown background of dry bushes.
cauliflower. b. Brown
(b) List the steps involved in the formation of new c. Natural selection.
species.
103. (a) Explain why the wing of a bat and the wing of
(c) How different races of human beings belong to the
bird are considered to be analogous organs.
same species?
(b) List two factors that lead to the formation of a
Ans : [CBSE 2013] new species.
a. Formation of newer varieties, e.g., Broccoli, Ans : [CBSE 2012]
cauliflower, red cabbage, etc. by man.
a. Design, structure and components are different.
b. Migration, gene flow, natural selection, new
Origins are not common.
species.
b. Genetic drift and natural selection.
c. Capable of interbreeding among themselves.
104. a.Name the scientist who gave the idea of evolution
100. What is speciation? Discuss any two factors that lead
of species by natural selection.
to speciation.
b. What conclusion did Mendel draw from his
Ans : [Delhi 2012] experiments about traits?
Speciation means creation of new species from pre c. Arrange the following according to evolution.
exiting ones. Cockroach, Mango tree, Gorilla, Fish
The two main factors which could lead to the Ans :
formation of a new species are natural selection leading a. Darwin
to accumulation of adaptation in geographically b. Traits are inherited independently.
separated populations of a species and development of c. Mango tree — Cockroach - Fish — Gorilla.
reproductive barrier among them.
105. a.What are fossils?
Complete separation of sub-populations of a
b. Explain the importance of fossils in evolutionary
spices (Genetic drift) and difference in way of Natural
relationship.
selection in them for many generations results in
speciation i.e. formation of new species that cannot Ans :
interbreed under natural conditions. a. Impressions of the body parts of the organisms
and preserved traces of the living organisms are
101. Fore limbs of amphibians, reptiles, birds and mammals
called fossils.
show similarity in their bones but Wings of bat and b. The presence of fossilized remains of the organism
bird don’t. What conclusion can be drawn from such is the evidence of existence of organisms million
years ago which have now become extinct. Fossils
 also help in determining the connecting links If a sperm with “X’ fuses with the ovum, female
between various groups and their origin from child is born and if a sperm with ‘Y’ chromosome fuses
their primitive ones. with the ovum, male child is born as shown below in
the cross.
106. What are fossils? What do they tell about the process
of evolution?
Ans : [Outside Delhi 2008, CBSE 2008 C]
The fossils can be defined as remains or impressions
of the hard parts of the past individuals in the strata
of the earth. Fossils helps in working out evolutionary
relationships. Fossils provide one of the most
acceptable evidences in support of evolution, because
we can study the evolutionary past of individuals in
Hence, we find that the sex of the child is actually
the form of their fossils. By studying fossils occurring
determined by the type of sperm that fuses with ovum
in different strata of rocks, geologists are able to
at the time of fertilization.
reconstruct the time course of evolutionary events.
Age of fossils can also be found by time dating using In this manner we can justify that the sex of the
isotopes of carbon (carbon dating). children is determined by what they inherit from their
father and not their mother.
107. “Only variations that confer an advantage of an
individual organism will survive in a population”.
Comment. FIVE MARKS QUESTIONS
Ans : [Delhi 2008 C]
According to Theory of Natural Selection, some 109. How do Mendel’s experiment show that traits are
variations are advantageous for an organism to inherited independently?
adapt better in the prevailing conditions of habitat. Ans : [All India 2016]
It makes it easy to obtain food and mating partner
Mendel carried out dihybrid crosses by crossing
by them. In this manner they are able to propagate
two pea plants differing in contrasting traits of two
more, transmitting their genes to next generation
characters. For example, he crossed a pea plant
and producing more individuals with similar genetic
having yellow colour and round seed characters with
makeup and phenotype.
another pea plant bearing green colour and wrinkled
Though according to Genetic Drift Theory, even seed characters. In the F2 generation, he obtained
those not having a variation that confers an advantage pea plants with two parental and two recombinant
also get to 5 survive but only in a small population. If phenotypes as yellow round and green wrinkled
due to an accident most of the individual with other (parental) and yellow wrinkled and green round
variation get removed, the organisms with leftover (recombinant). This indicated that traits separated
variation get to propagate and survive under such from their original parental combinations and got
circumstances. inherited independently.
Hence it is wrong to say that only variations that
confer an advantage of an individual organism will
survive in a population.

108. Explain the manner in which sex is determined in

human beings? [Delhi 2008 C]
or
Explain how equal genetic contribution of male and
female parents is ensured in progeny?
Ans : [CBSE 2011] [Delhi 2012]
The sex of the child is determined at the time of
fertilization when male and female germ-cells (gametes)
are fused to form a zygote. The sex is determined by a
specific pair of chromosomes called sex-chromosomes.
In female human being, this pair consists of two similar
(homologous) chromosomes denoted as XX. Hence,
females produce only one type of gametes (Ova/ eggs)
each having an “X’ chromosome.
Whereas male human being has two different types 110. Define evolution. How does it occur? Describe how
of sex chromosomes i.e., X, Y (heterologous) having fossils provide us evidences in support of evolution.
different sizes and shapes. Hence male produces two Ans : [All India 2016]
different kinds of gametes (sperms). Half of them have
Evolution is the formation of more complex organisms
‘X’ chromosome and half have Y” chromosome.
from pre-existing simpler organisms over a certain
 period. Accumulation of variation in genetic material sense light.
forms the basis of evolutionary processes.
113. a.What are monohybrid and dihybrid cross?
Fossils provide a unique view into the history of b. How Mendel proved that tallness is the dominant
life by showing the forms and features of life in the trait and dwarfness is recessive in a pea plant?.
past. Fossils tell us how species have changed across Explain with the help of a monohybrid cross.
long periods of the Earth’s history.
Ans : [CBSE 2016]
Importance of fossils in the evolutionary process:
a. Some invertebrates living on the sea bed died and a. A monohybrid cross is the cross between two
were buried in the sand. homozygous parents, which differ in only one
b. More sand was accumulated and formed , contrasting trait in F2 generation ratio 3:1.
sandstone under pressure. A dihybrid cross is a cross between two
c. After millions of years, dinosaurs living in the area heterozygous parents which differ in two
died and their bodies were buried in the mud. contrasting traits. This type of cross yields a
d. The mud got compressed into the rock, just above phenotypic ratio of 9 : 3 : 3 : 1 in F2 generation.
the rock containing earlier invertebrate fossils. b. Mendel took pea plants with different
e. Again millions of years later, the bodies of horse- characteristics - a tall plant and a short plant,
like creatures dying in the area were fossilised in produced progeny from them and calculated the
the rocks above the earlier rocks. percentage of tall or short progeny.
f. Much later, because of erosion and water flow,
some rocks wore out and exposed the horse-like
fossils.

111. Give five points to show the significance of variations.

Ans : [CBSE 2016]
a. Variations help an organism to get adapted to the It was found that all plants were tall. This
changing environment. proves that tallness is the dominant trait while
b. Variations lead to evolution through natural dwarfness is the recessive trait.
selection and adaptation. 114. What are fossils? How are they formed? Describe in
c. During sudden change in the environment only brief two methods of determining the age of fossils.
those variants will make the population of that State any one role of fossils in the study of the process
particular species which can withstand such of evolution.
changes.
d. Variations result in more genetic vigour, i.e., Ans : [CBSE 2016]
organism emerges as a strong species maintaining Fossils are preserved remains or impressions of pre-
its large population. historic organisms in the different strata of the earth’s
e. Variations make an organism to be resistance to crust.
diseases and environmental fluctuations. or
Fossils are dead remains of animals and plants from
112. a.“Evolution has occurred in stages.” Justify the remote past.
statement.
b. Differentiate between eye and eyespots. Which Fossils are formed when dead organisms are not
animal possesses eyespots? completely decomposed. The organisms may get
trapped in resins of tree, lava of volcanoes or hot mud
Ans : [CBSE 2016] which when hardens, retains the animal’s parts thus,
a. “Evolution has occurred in stages” it is said forming fossils.
because the process of evolution has took place Two methods of determining the age of fossils:
over a long period of time. The complex organs a. Relative method: By estimating the age of the
are created bit-by-bit over generations. layer of earth’s crust where the fossil is found.
There was increasing complexity of the Fossils near the surface are recent and those in the
organs. For example, eye was present in the deeper layers are more ancient.
earliest organism as eyespot which got developed b. Radio-carbon dating method: By detecting the
into a more complex and evolved eye. ratios of different isotopes of carbon in the fossils.
Further there are some organs in the human Fossils help in determining the connecting links
body which are present in the reduced form and between various groups and their origin from their
do not perform any function, e.g., nictitating primitive ones, e.g., Archaeoptyrx.
membrane of the eye, vermiform appendix, third
pair of molars etc. 115. How many pairs of chromosomes are present in human
Similarly, during the course of evolution, some beings? Out of these how many are sex chromosomes?
structures changed their function. So we can see How many types of sex chromosomes are found in
that evolution has occurred in stages over a long human beings?
period of time. “The sex of the new-born child is a matter of chance
b. Eye is a complex structure made-up of different and none of the parents may be considered responsible
tissues which can see image as well as light for it”. Draw a flow chart showing determination of
whereas eyespots are merely dot-like structure to sex of a new-born to justify the statement.
 Ans : [Delhi 2015] beetle eaten up by crow, leading to increase in the
a. 23 pairs of chromosomes. population of green beetle.
b. One pair, two types. Artificial selection: It is the artificial mechanism of
c. selecting the breeds having desirable characters to
bring about major changes in plant and animals.
Example, different vegetables generated from wild
variety of cabbage.

119. a.What is geographical isolation?

b. Illustrate formation of a species with the help of
an example where individuals are very different
from each other and one capable of reproduction
among themselves.
116. What is speciation? List four factors that could lead Ans : [CBSE 2012,13]
to speciation. Which of these cannot be major factors a. Geographical isolation is the isolation of
in the speciation of a self pollinating plant species? population by physical barriers such as stretches
Explain. of water or mountain ranges.
Ans : [Foreign 2015] b. There is a population of red beetles living in
a mountain area covered with green bushes.
Speciation - formation of new species from pre-existing
Various sub-population in the large-population
ones.
exists in the neighbourhood. Individuals of
Factors - (1) Mutations (2) Natural selection (3)
a sub¬population reproduce sexually among
Genetic drift (4) Geographical Isolation
themselves and numerous variations accumulate
Geographical isolation cannot be a major factor in these sub-populations of red beetles.
in the speciation of a self pollinating plant species. There may be some reproduction among
Reason - physical barrier cannot be created in self these sub-populations. If a beetle from one sub-
pollinating plants. population strays into other’s area and some
individuals from one sub¬population may be
117. a.Why do we say that homozygous plants produce carried by predators to the area of other sub-
pure progeny? population, then random reproduction takes
b. Define heterozygous. place. It may lead to migration of genes from one
c. Explain how the process of speciation take place. sub¬population to other.
Ans : [CBSE 2014]
120. Identify male and female in the figures given below.
a. Because of presence of same set of genes.
b. Having different pair of genes. Also fill in the blanks 3 to 8 and then clarify about
c. (i) Natural selection. the misconception that mother and not father is
(ii) Geographical isolation, reproductive isolation. responsible for bearing daughters and not sons.
(iii) Genetic drift.
(iv) Accumulated variations causing changes in
the DNA of germ cells to an extent, such
as a change in the number of chromosomes.
Due to this, the germ cells of the two groups
cannot fuse with each other. This results in
the emergence of a new species.

118. Give differences between:

a. Heredity and variations.
b. Dominant and recessive traits,
c. Natural and artificial selection.
Ans : [CBSE 2014]
a. Heredity: It is the transmission of characters from
parents to the next generation.
Variations: The changes that occur in the DNA of
an organism because of mutations, or by chance. Ans : [Sample Paper 2010]
b. Dominant: The trait which is able to express
itself even in the presence of contrasting trait. It 1. Male 2. Female
appears in all the progenies in Fj generation. 3. X and Y 4 X and X
Recessive: The trait which can express itself only 5. XX 6 XX
in homozygous condition. It doesn’t appear in Fj 7. XY 8 XY
generation. A child who inherits ‘X’ chromosome from father
c. Natural selection: Is the gradual natural process will be a girl and the one who inherits ‘Y’ chromosome
by which any biological traits become either more from father will be a boy.
or less common in a population. Example, red
121. a.In which form the traits are transferred from F1 - RrYy
parent to the offspring? Ratio - 9 : 3 : 3 : 1
b. Mention the two processes that essentially J occur b. To study the independent inheritance of two traits
in sexual reproduction? in subsequent generation.
c. How the number of chromosomes is retained in a c. F1 progeny exhibited both the dominant traits.
species? F2 exhibited parental traits along with new
Ans : [Delhi 2013] mixtures/recombinants.
a. Chromosomes - thread like structures made up of 123. Woman are often blamed for bearing daughters. As a
DNA found in the nucleus. student with knowledge in science how will you explain
b. Formation of gametes that involves reducing it to your fellow students that the sex of the child is
the chromosome number to half and genetic not determined by mother’s genetic contribution?
recombination. Ans :
Fusion of gametes to maintain the chromosome
number characteristic of that species. Sex of the child is not determined by mother’s genetic
c. The original number of chromosomes becomes contribution. The sex is determined by a specific
half during gamete formation. Hence, when pair of 7 chromosomes called sex-chromosomes. In
the gametes combine, the original number of female, this pair consists of two similar (homologous)
chromosomes gets restored in the progeny, (or chromosomes denoted as XX. Hence, females produce
same thing explained in the form of a flow chart). only one type of gametes (Ova/eggs) each having an
‘X’ chromosome.
122. Given below is the experiment carried out by Mendel Whereas male human being has two different types
to study inheritance of two traits in garden-pea. of sex chromosomes i.e., X, Y (heterologous) having
different sizes and shapes. Hence male produces two
different kinds of gametes (sperms). Half of them have
“X’ chromosome and half have ‘Y’ chromosome.
If a sperm with ‘X’ fuses with the ovum, female
child is born and if a sperm with ‘Y’ chromosome fuses
with the ovum, male child is bom as shown below in
the cross. Therefore, the father’s genes is responsible
for the determination of the sex of the child.

a. Fill in the boxes with appropriate answer.

b. Why did Mendel carry out an experiment with
two traits?
c. What were his findings with respect to inheritance
of traits in Fj and F2 generations?
d. What do you conclude from this experiment?
Ans : [Sample Paper 2010]
a. Gametes - Ry, rY
Chap 11 : Human Eye and The Colorful World www.cbse.online

CHAPTER 11
Human Eye and The Colorful World

1. ONE MARK QUESTIONS For a human eye, there is a near point, 25 cm. If the
distance of the object is lesser than this distance, eye
cannot see object clearly.
1. Name the essential parts of human eye,
11. When you enter from a bright sunshine into a dark
Ans : [CBSE 2016] room, you are not able to see clearly for sometime,
(a) Retina (6) Eye lens (c) Cornea (d) Pupil (e) Iris why?
Ans : [Delhi 2015]
2. Which liquid fills the space behind the cornea?
In bright light, pupil had become small.
Ans : [Delhi 2016]
Aqueous humour is filled in the space behind the 12. On what factor the colour of the scattered light
cornea. depends?
Ans : [CBSE 2015]
3. Which part of the eye controls the amount of light
entering the eye? The colour of the scattered light depends on the size
of scattered particles.
Ans : [CBSE 2016]
Pupil controls the amount of light entering the eye. 13. What is Presbyopia ?
Ans : [CBSE 2014]
4. What is eye lens made of ?
Presbyopia is a kind of eye defect in old persons due
Ans : [CBSE 2016]
to ageing. It happens due to decrease in flexibility of
Eye lens is made of transparent and flexible jelly like eye lens and weakening of ciliary muscles.
material.
14. What is twinkling of stars due to?
5. How is the sense of vision carried from the eye to the Ans :
brain?
Twinkling of star is due to atmosphere refraction.
Ans : [CBSE 2016]
Through optical nerve, sense of vision is carried from 15. Define dispersion of white light.
eye to the brain. Ans : [CBSE 2014]
6. Which liquid fills the space between eye lens and The splitting of white light into its constituents seven
retina? colours is called dispersion of light.
Ans : [All India 2015] 16. What kind of lens is used in the spectacles of a person
Vitreous humour. suffering from myopia (near sightedness)?
Ans : [CBSE 2014]
7. Why is blind spot so called?
A diverging lens/concave lens is used for a person
Ans : [CBSE 2015]
suffering from near sightedness/ myopia.
An image formed at this point is not sent to brain.
17. Name the part of the human eye that helps in changing
8. What is the number of receptors contained in the the focal length of the eye lens.
retina? Ans : [All India 2013]
Ans : [CBSE 2015]
Ciliary muscles help in changing the focal length of
Retina contains more than 125 millions receptors the eye lens.
which are of two types, rods and cones.
18. Write the value of near point of distinct vision for
9. What is meant by far point? normal eye.
Ans : [CBSE 2015] Ans : [CBSE 2013]
The farthest point upto which an normal human eye For a normal human eye the value of near point of
can see objects clearly is known as far point. distinct vision is 25 cm.
10. Why can you not see an object clearly if it is placed 19. What is the role of pupil in a human eye?
very close to your eye? Ans : [CBSE 2013]
Ans : [All India 2015]
 Pupil regulates and controls the amount of light depends. Why does the sky appear dark in space?
entering in the eyes. Ans : [CBSE 2016]
20. What is the range of vision for a normal human eye? Scattering of light depends on the presence of
Ans : [CBSE 2013] atmosphere which contains water droplets, molecules
of air, smoke and dust particles.
Range of vision is 25 cm to infinity.
In the space, there is no atmosphere to scatter
21. Name the two phenomena involved in the formation light.
of rainbow.
30. How can change of size of eyeball be one of the reason
Ans : [CBSE 2012]
for: (a) Myopic (b) Hypermetropic
The phenomena involved in formation of rainbow are
Compare the size of eyeball with that of a normal
dispersion and total internal reflection and refraction.
eye in each case. How does this change of size affect
22. Name the component of white light that deviates the the position of image in each case?
least and the most while passing through a prism. Ans : [All India 2016]
Ans : [CBSE 2012] (a) The eye suffering from myopia, has long eye ball
Red colour deviates the least and violet colour deviates than that of normal eye due to which the retina
the most. is at a larger distance from the eye lens. This
results in the formation of the image in front of
23. A person is advised to wear spectacles with concave the retina.
lenses. What type of defect of the vision is he suffering (b) The eye suffering from hypermetropia has short
from? eye ball than that of normal eye due to which the
Ans : [CBSE 2012] retina is smaller distance from the eye lens. This
results in the formation of the image behind the
Myopia. retina.
24. Name the part responsible for the power of 31. Sushil went to an eye specialist for check up. He
accommodation of the eye. prescribed him to use spectacle lens of + 0.5D power.
Ans : [CBSE 2012] a. Name the defect of vision he is suffering from.
Ciliary muscles help for the power accommodation of b. Find the focal length of spectacle lens.
the eye. Ans : [CBSE 2015]

25. Name the condition resulting due to the eye lens a. Hypermetropia.
becoming cloudy. b. Power of spectacle P = + 0.5D
Ans : [CBSE 2012] f = 1 =+ 1 m
P 0.5
Cataract.
or f =+ 2 m positive sign means it is a convex
26. Why sky appears dark to the passengers flying at high lens.
altitudes?
32. State the function of pupil and ciliary muscles.
Ans : [CBSE 2012]
Ans : [CBSE 2015]
There is no atmosphere at high altitudes. Hence no
scattered light can reach to the eye. a. Pupil controls the amount of light entering the
eye.
27. A person suffering from an eye defect uses lenses of b. Ciliary muscles help in accommodation of power
power – 1D. Name the defect he is suffering from and of eye lens.
the nature of lens used.
33. A child sitting in a classroom is not able to read
Ans : [CBSE 2012]
clearly the writing on the blackboard.
He uses a concave lens (negative power) because he is a. Name the type of defect from which his eye is
suffering from myopia. suffering.
b. With the help of a ray diagram show how this
28. Which colour of white light suffers (i) least deviation
defect can be remedied.
and (ii) maximum deviation when a beam of white
Ans : [Delhi 2015]
light passes through a glass prism?
Ans : [CBSE 2011] a. Myopia
b. Myopia can be remedied by using concave lens.
Longer wavelength light (red) suffers least deviation
and shorter wavelength (violet) suffers maximum
deviation when white light is passed through a prism.

TWO MARKS QUESTIONS

29. Mention the factor on which scattering of light

 If another identical prism is placed in inverted position
in front of a prism then dispersed colours obtained
from first prism get recombine to produce white light.

34. What is meant by persistence of vision?

Ans : [All India 2014] 40. Explain why do stars twinkle and planets do not?
Ans : [CBSE 2012]
On removing object seen, its impression persists on
the retina for 161 th second. The inability of human The light coming from star get refracted through the
brain to perceive more than two images formed on the atmospheric layers. Due to this, the star appear slightly
retina within interval of 161 th of a second is called higher than its actual position. Since the densities of
persistence of vision. In this case, both the images atmospheric layers changes frequently and hence the
merge and give a sensation of continuity. position of the star appear changes continuously stars
are very distant point-sized objects. As the path of
35. List four common defects of vision that can be rays of light coming from star is continuously changes.
corrected with the use of spectacles. So sometimes light enters into our eyes and some
Ans : [Delhi 2013] times it faints. This is twinkling of the star. Since
(i) Myopia (ii) Hypermetropia (iii) presbyopia (iv) planets are closer to us, their size is also big. Our
Astigmatism. eyes receive light from different points of the planets.
Hence planets do not twinkle.
36. (a) Explain how a normal human eye is able to see
41. List two causes leading to myopia of the eye. Draw
distinctly the object placed at a distance as well
as those placed at a nearer distance. ray diagrams to show the image formation in case of
(b) What is the far point and near point of a normal defective eye and corrected eye.
human eye? Ans : [CBSE 2012]
Ans : [CBSE 2013] Causes of Myopia
(a) Ciliary muscles change the curvature of eye lens as a. Excessive curvature of cornea
per requirement of the eye. This changes the focal b. Elongation of eye ball.
length of eye lens. When muscles are relaxed, lens
becomes thin and distant objects are seen clearly.
While seeing closer objects, muscles contract, this
thickens the eye lens and focal length decreases.
(b) Far point — Infinity. Near point — 25 cm from
the eye.

37. What is meant by least distance of distinct vision?

How does this vary between the very young and old
people?
Ans : [CBSE 2013]
42. (a) What is the least distance of distinct vision for
Least distance of distinct vision is the minimum
distance between eye and object to see it clearly. the normal eye?
(b) Does the above distance increase or decrease for
In young, the least distance of distinct vision is long sighted eye? Give reason for your answer
lesser and for old people it is more. with diagram.
38. Define dispersion of white light and name the colours Ans : [CBSE 2012]
of white light in order. (a) For a normal human eye, the least distance of
Ans : [CBSE 2012] distinct vision is 25 cm.
(b) Least distance of distinct vision increases for long
When white light is passed through a prism, it splits
sighted eye. A hypermetropic eye can see upto
into its seven constituent colours. Splitting of white
infinite distance, which is more than 25 cm.
light into its constituent colours is called dispersion.
Seven constituent colours are – violet, indigo, blue,
green, yellow, orange and red. (VIBGYOR).

39. Describe an experiment to discuss the recombination

of dispersed light.
Ans : [CBSE 2012]
 through a glass prism.
Ans : [CBSE 2012]
a. Splitting of white light into its constituent colours
when passed through a prism called dispersion of
light.
b. Violet colour deviates the most while passing
through the glass prism.

48. Why does it take sometimes to see the objects in a dim

room when we enter the room from bright sunlight
outside?
Ans : [CBSE 2011]
In bright sunlight, pupil of eye contracts to control the
light. When we enter a dim room, pupil takes some
43. A person needs a lens of power –2.5 dioptres for
time to expand to allow more light to see the objects
correcting his vision. Name the defect of vision he
clearly.
is suffering from. Which lens will he be using for the
correction? Also, find the focal length of lens. 49. Why does the clear sky appear blue? How would the
Ans : [CBSE 2012] sky appear in the absence of earth’s atmosphere?
Ans : [CBSE 2011]
P = - 2.5D
The person using a lens of negative focal length Scattering of light \ l1 where l is the wavelength
4

of light, i.e. least wavelength will scatter more and

f = 1 = - 1 = - 0.4 m =- 40 cm vice versa. Blue colour light has shorter wavelength
P 2.5
Here negative focal length means he uses a concave and hence scattered more than other colours. In space,
lens. there is no atmosphere hence no scattering of light
happens in the space so space appears black.
44. Name the part of the eye where image is formed by
the eye lens. What is the nature of the image formed? 50. Why do we observe difference in colours of the sun
How is this image sent to the brain? during sunrise, sunset and noon?
Ans : [CBSE 2012] Ans : [CBSE 2011]

Retina. During the sunrise or sunset, the sun is at horizon. Most

Image on the retina is inverted and real. Optic nerve of the blue light and other light of shorter wavelength
sends the image to the brain. are scattered most. Only the longer wavelength (red)
reaches to us. That’s why sun appears red during the
45. Explain how a normal human eye is able to see sunrise or sunset.
distinctly the object placed at a distance as well as At noon, the Sun appears white because it is at
those placed at a nearer distance. What is the far our head and all wavelength reaches to us due to little
point and near point of a normal human eye? of the blue and violet colours are scattered due to
Ans : [CBSE 2012] least distance travelled by fight.
To see a near object, the focal length of the eye should
51. Why do we observe the seven colours when white light
be small and vice versa. The focal length of the eye
passes through a glass prism? Which component of
lens can be adjusted by ciliary muscles. When one see
white light deviates the least?
near object, ciliary muscles decreases the focal length
and for distant object, ciliary muscles increases the Ans : [CBSE 2011]
focal length. Far point — Infinity. Since angle of deviation for different colour is different
Near point — 25 cm from the eye. hence different colour suffers different deviation.
Deviation for red colour is minimum.
46. An old person is unable to see clearly nearby object as
well as distant objects, (i) What defect of vision is he 52. Draw a neat diagram to show the refraction of a light
suffering from? (ii) What kind of lens will be required ray through a glass prism, and label on it the angle of
to see clearly the nearby as well as distant objects? incidence and angle of deviation.
Give reason. Ans : [CBSE 2011]
Ans : [CBSE 2012]
(i) Old person is suffering from presbyopia.
(ii) He cannot see near objects as well as distant
objects, so he has to use bifocal lenses which
consists of concave and convex lenses both.

47. What is dispersion of light? Name the (i) component

of white light that deviates the least, (ii) component
of white light that deviates the most, while passing
PE–Incident ray +i –Angle of incidence
 EF–Refracted ray +r –Angle of refraction Correction: Using a concave lens myopic
FS–Emergent ray +e –Angle of emergence
+A –Angle of prism +D –Angle of deviation

53. (a) What is ‘power of accommodation of the eye?

(b) What happens to the image distance when the
object being viewed is moved away from the eye?
Ans : [CBSE 2011]
(a) Power of accommodation of the eye means the
ability to change the focal length of the eye lens
to see near and distant objects.
(b) Image distance remains fixed which is equal to
distance between retina and eye lens.

54. (a) What is meant by least distance of distinct vision?

(b) How does the thickness of the eye lens change
when we shift looking from a distant tree to (b) Due to atmospheric refraction stars twinkle. The
reading a book? density of atmospheric layers keep changing due to
Ans : [CBSE 2011] which point sized star sometimes appear brighter
(a) Least distance of distinct vision means the or dimmer with changing position. Due to this,
minimum distance upto which an eye can see stars appears twinkling.
clearly. 57. (a) Write the function of each of the following parts
(b) To see distant object focal length of eye lens must of human eye:
be more so it becomes thinner when we want to (i) Cornea (ii) Iris
read a book eye lens is comparatively thicker. (iii) Crystalline lens (iv) Ciliary muscles
55. A 14 year old student is not able to see clearly the
(b) Why does the sun appear reddish early in the
questions written on the blackboard placed at a morning? Will this phenomenon be observed by
distance of 5 m from him. an astronaut on the Moon? Give reason to justify
a. Name the defect of vision he is suffering from. your answer.
b. With the help of labelled ray diagrams show how Ans : [Delhi 2018, 2017]
this defect can be corrected. (a) Function of Human eye:
c. Name the type of lens used to correct this defect. (i) Cornea focuses light ray to enter the eye.
Ans : [CBSE 2007] (ii) Iris control and regulate amount of light
a. Myopia entering the eye and control the size of pupil.
b. (iii) Crystalline lens is like a convex lens which
converge light rays on the retina.
(iv) Ciliary muscles adjust focal length of eye lens
by contraction and relaxation so that sharp
image can be obtained on the retina.
(b) During morning and evening time, sun is at the
horizon, sunlight has to travel longer distance in
atmosphere. Violet and blue colours etc. of shorter
wavelength scatter in the space only. The longer
wavelength red colour reaches to the observer on
earth and sun appears reddish.
No, because there is no atmosphere on moon and
c. Concave lens no scattering of light takes place there.

58. (a) With the help of a suitable diagram explain why

FIVE MARKS QUESTIONS the Sun is visible to us two minutes before the
actual sunrise and two minutes after the actual
sunset.
56. (a) A student is unable to see clearly the worlds
(b) Name the phenomenon responsible for apparent
written on the blackboard placed at a distance of
flattening of the Sun’s disc at sunrise and sunset.
approximately 3 m from him. Name the defect of
vision the boy is suffering from State the possible Ans : [CBSE 2016]
causes of this defect and explain the method of (a) The duration of the day becomes approximately 4
correcting it. minutes longer due to atmospheric refraction. We
(b) Why do stars twinkle? Explain. can see the sun when it is below the horizon in the
Ans : [Delhi 2018] morning. The rays of light from the sun below the
horizon(s) reach to our eyes due to refraction of
(a) Defects of vision: Myopia or short sightedness.
light 2 minutes before it actually rises. Similarly
Reasons: Excessive curvature of eye lens and
the sun can be seen about 2 minutes after it
elongation of eye ball.
 actually set. Thus the duration of day time interacts with particle of matter. When sunlight
increases by 4 minutes (2 minutes each time at strikes molecules in atmosphere, the light is
the time sunrise or sunset). redirected in many direction.
b. Scattering of blue colour is most due to shorter
wavelength, where as scattering of red colour is
least. All colours scattered in the sky and red
colour light reaches to earth, due to this sun
appears reddish.

59. Study the diagram and answer the questions the 62. With the help of scattering of light, explain the reason
follows : for the difference in colours of the Sun as it appears
Ans : during sunrise/sunset and noon.
Ans : [CBSE 2015]
At the time of sunrise or sunset it appears red where
as at noon it appear white when it is overhead
because at sunrise or sunset blue colour and other
shorter wavelength light get scattered away while
passing through the atmosphere. Scattering of longer
a. Identify the defect of vision represented by this wavelength is least which reach to the earth. Due to
diagram. this sun appears red during morning and evening time.
b. List the two possible causes of this defect. When sun is overhead at noon, sun rays travels
c. With the help of ray diagram explain how this smaller distance, due to little scattering of blue and
defect can be corrected. violet colour wavelength almost all wavelengths reach
Ans : [Delhi 2016] to earth and due to this sun appears white.
a. The defect of vision is hypermetropia. 63. State the cause of dispersion, when white light enters
b. (i) increase in focal length of eye lens a glass prism. Explain with a diagram.
(ii) shortening of eye ball.
Ans : [All India 2014]
c. Hypermetropia can be corrected by using convex
lens. When white light passes through a prism it splits into
its constituent colours, because each coloured light has
different speed in prism. Prism has different refractive
index for these light rays and so deviates through
different angles when emerge out from the prism.
Deviation for violet colour (shortest wavelength) is
most and for red colour (largest wavelength) deviation
is least.

60. A person can see distant signboards clearly but cannot

read clearly a book which is at 25 cm from his eye.
Giving reason identify the defect. Draw a labelled ray
64. (a) Calculate maximum power of accommodation of a
diagram to illustrate this defect and its correction.
person having normal vision.
Ans : [CBSE 2016]
(b) A person needs to use glasses for reading
Eyes defect is hypermetropia. Its causes are due to newspaper. Identify the defect in her vision and
a. shortening the eye ball the type of lens she would need to correct it.
b. increase in focal length of eye lens. (c) Sometimes when we enter into a dark room from
bright sunlight we are unable to see objects
clearly. Why?
Ans : [CBSE 2014]
(a) Least distance of distinct vision for a normal eye
D = 25 cm .
61. What is meant by scattering of light? Use this P = 1 = 100 = 4D
phenomenon to explain why the clear sky appears f 25
blue or the sun appears reddish at sunrise. For a person having normal vision, the power of
accommodation is 4 D.
Ans : [CBSE 2015]
(b) Hypermetropia, to correct hypermetropia convex
a. Scattering of light is phenomenon by which beam lens is needed.
of light is spreaded in many direction when it
 (c) In bright light the pupil contract its size becomes
small to control the light, but when we enter into
a dark room it take sometime for the pupil to
expand to allow more light in dark room.

65. State one function each of iris, pupil, and cornea. It can be corrected with the help of a convex lens
Ans : [CBSE 2014] as shown.
a. Iris: It controls the amount of light entering the
eye by changing the size of pupil.
b. Pupil: Pupil is a part of the eye through which
light enters in the eye.
c. Cornea: It is a thin membrane which covers the
eye ball. Light enters the eye through cornea 69. A person is unable to read a book clearly when kept
where it is refracted most. at a distance of 25 cm from his eye. Name the defect.
How can it be corrected? Draw ray diagrams for (i)
66. (a) Explain the phenomenon of scattering of light.
defective eye (ii) corrected eye and explain them.
State the factor on which colour of scattered light
depends. Ans : [CBSE 2013]
(b) List any two natural phenomenon based on The person cannot read a book at a distance of 25 cm
scattering of light. from his eyes. So he is suffering from long sightedness/
Ans : [CBSE 2014] hypermetropia. It can be corrected by using convex
lens of suitable focal length.
(a) Scattering of light is the phenomenon due to which
light gets deflected by the atoms or molecules
of different atmospheric gases and suspended
particles present in atmosphere. Scattering
depends upon size of the particles of the medium
through which light passes.
(b) Two natural phenomenon based on scattering
are (i) Reddish colour of sky during sunrise and
sunset, (ii) Blue colour of sky.

67. A person cannot see objects farther than 12 m from

the eye clearly. Name the defect of vision he is suffering
from and the lens that should be used for correction of
this defect. Illustrate with the help of a diagram, how
this lens will correct the defective vision?
Ans : [CBSE 2011, 2013]
He is myopic. Myopia can be corrected by using
concave lens.

70. With the help of a diagram, explain the formation of

a rainbow in the sky.
Ans : [CBSE 2012]
The water droplets in the atmosphere act like small
prisms. These droplets refract and disperse the
incident sunlight, then reflect it internally and finally
refract it again when it comes out of the rain drop.
Due to distortion of sunlight and internally reflection,
different colours reach to the observer.
68. A person cannot read a book at distances less than
50 cm. Name the defect of vision he is suffering from.
How can it be corrected? Draw ray diagrams to show
the image formation:
a. by defective eye and
b. after using corrective lens.
Ans : [CBSE 2011, 2013]
a. Either the hypermetropic eyeball is too short or
b. The ciliary muscle is unable to change the shape
of the lens enough to properly focus the image i.e.,
the focal length of the eye lens is too long. This 71. (a) What is meant by dispersion of white light? Draw
defect is called hypermetropia. a diagram to show the dispersion of white light by
 a glass prism. e. Due to absence of atmosphere in the space, there
(b) Light of two colours A and B pass through a is no scattering and hence space appears black/
prism. A deviates more than B from its path of dark.
incidence. Which colour has a higher speed in the
prism? 74. (a) If a person wears lens of power - 6D for distant
vision and for correcting his near vision he needs
Ans : [CBSE 2011]
a lens of +2D. Determine the focal length of the
(a) Splitting of white light into its constituent colours lenses in both the case.
when it is passed through a prism is called (b) Give reason for the following natural phenomenon:
dispersion of white light. (i) Stars twinkle
(ii) Planets do not twinkle
(iii) Stars appear raised in the sky.
Ans : [CBSE 2016]

(a) (i) P1 = - 6D as f1 = 1 =- 1 m
P1 6
f1 = - 100 cm = - 16.66 cm
6
(ii) P2 = + 2D as f2 = 1 =+ 1 m
P2 2
(b) B f2 = 50 cm
(b) (i) Due to continuous changes in the densities of
the atmospheric layers the apparent position
FIVE MARKS QUESTIONS of the star also changes; which make the
light coming from the distant point sized
star brighter and dimmer. The light coming
72. (a) A student is unable to see clearly the words
from the stars therefore gives a shaking
written on the black board placed at a distance of
appearances, which gives the impression of
approximately 3 m from him. Name the defect of
twinkling of a star.
vision the boy is suffering from. State the possible
(ii) Since the planets are closer to us. Due to this
causes of this defect and explain the method of
they appear a combination of large point-sizes
correcting it.
source of light, and change in the path of light
(b) Why do stars twinkle? Explain.
coming from the planets is not significant. So
Ans : [CBSE 2017] planets do not appear twinkling.
(a) He is suffering from myopia. (iii) Due to atmospheric refraction, a star appears
Causes of myopia: to be slightly higher than its actual position
(i) elongation of eye ball. in sky.
(ii) excessive curvature of cornea.
Concave lens of suitable power is used to correct 75. (a) State the reasons which lead to hypermetropia.
myopia. With the help of suitable diagram, explain this
(b) Light coming from stars when enter in the Earth’s defect of vision and its correction.
atmosphere suffers refraction from the atmospheric (b) Draw diagram of an experimental arrangement for
layers. Since the densities of atmospheric gases observing scattering of light in colloidal solution.
changes frequently. Since the stars are point sized Name the two chemicals used in this activity.
and at a far distance so sometimes star appear Ans : [All India 2015]
brighter and sometimes dimmer which gives the a. In hypermetropia a person cannot see near by
impression as the stars twinkling. objects clearly. Its is due to shortening of the eye
ball or due to increase in focal length of eye lens.
73. Account for the following:
To correct hypermetropia, a convex lens of suitable
a. Part of the human eye that helps in changing the
focal length is needed.
focal length of the eye lens.
b.
b. The condition resulting due to the eye lens
becoming cloudy.
c. The factors on which colour of the scattered white
light depends.
d. The range of vision of a normal eye.
e. The sky appears dark to the astronauts in the
space.
Ans : [CBSE 2016]
a. Ciliary muscles. 76. What is meant by scattering of light? Mention the
b. Cataract. factor on which it depends. Explain why the colour of
c. Size of the suspended particles in the medium the clear sky is blue? An Astronaut in space finds sky
through which white, light passes. to be dark. Explain reason for this observation.
d. 25 cm to infinity is the range of vision of normal Ans : [CBSE2015]
eye. (a) Scattering of light is the phenomenon due to
 which light gets deflected by the atoms, molecules prism. Collect these coloured lights on a screen or
or particles of the medium when light falls on white sheet of paper. This prove that white light
them. These are known as scatterer particles. is made up of seven colours.
(b) Factors on which scattering depends are the size (b) Violet colour deviates most whereas red colour
of the atoms, molecules of the scatterer. deviates least because they have different speeds
(c) When sunlight falls on the atoms or molecules of in prism they have different refractive indices and
the gases shorter wavelengths J like of blue colour hence have different angle of deviation.
get scattered more due to which sky appears blue.
In space there is no atmosphere, so there is 80. (a) Explain why colour of clear sky appears blue
no scattering hence the sky appears dark/black. during the day with the help of diagram.
(b) Explain why Sun looks reddish at the time of
77. (a) How does refraction take place in the atmosphere? sunrise and sunset.
Why do stars twinkle but not the planets? Ans : [CBSE 2014]
(b) State any two effects of atmospheric refraction on
(a) Due to scattering of blue colours by the dust
the sun as observed from the earth.
particles present in the atmosphere.
Ans : [C8SE2015] (b) During the Sunrise or Sunset, Sun is at the
(a) Due to change in the density of atmospheric layers horizon, and sunlight travels a longer distance
when light travel through them gets refracted. It in the atmosphere. Due to this all colours get
is known as atmospheric refraction. Due to this scattered except red which reaches to the eye of
atmospheric refraction intensity of light, coming the observer to whom sun appears reddish in the
from a point sized star same times becomes more morning or evening.
and sometimes less, which gives the appearance of
twinkling of the star.
(b) (i) Sun can be seen two minute prior it rises and
two minute before it sets.
(ii) Twinkling of star.

78. Draw a neat labelled diagram of the structure of the

human eye and mention the functions of any four
parts.
Ans : [CBSE 2015] 81. A person cannot see the objects distinctly, when
placed beyond 2 m.
a. Identify the eye defect.
b. Give two reasons for this defect.
c. Calculate the power and nature of the lens he
should be using to see the distant objects clearly.
d. Draw the ray diagrams for the defective and the
corrected eye.
Ans : [CBSE 2011, 2013]
a. Myopia.
b. Elongation of eye ball or excessive curvature of
a. Cornea: A thin membrane which covers the eye cornea.
ball which allows the light to enter and refracts
c. P = 1 = 1 = - 0.5D
the light to focus it as the crystalline lens. f -2
b. Eye Lens: It is a convex lens made of transparent He will be advised to used a concave lens of power
and flexible jelly like material. Its curvature is – 0.5 D.
adjusted by ciliary muscles. d.
c. Iris: It controls and regulates the light entering
the eye by changing the size of pupil.
d. Pupil: It is a hole in the middle of the iris through
which light enters the eye.

79. (a) Demonstrate an activity with a well labelled

diagram to prove that white light is made up of
seven colours.
(b) Which colour of light bends least and which one
the most while passing out from the prism. Also
state the reason for the same.
Ans : [CBSE 2014] 82. A person cannot see the objects distinctly, when
(a) To demonstrate that white light is made up of placed at a distance less than 50 cm.
seven colours, take a prism. Allow white light to a. Identify the defect of vision.
fall on its one focus through a pin hole. Rotate the b. Give two reasons for this defect.
prism until the coloured light emerge out from the c. Calculate the power and nature of the lens he
 should be using to see clearly the object placed at
a distance of 25 cm from his eyes.
d. Draw the ray diagrams for the defective and the
corrected eye.
Ans : [CBSE 2011]
a. Hypermetropia.
b. Decrease in power of eye lens or shortening of eye
ball. 84. (a) Explain the following terms used in relation to
defects of vision and corrections provided for
c. u = - 25 cm, v =- 50 cm
them:
1 = 1 - 1 =- 1 + 1 (i) Myopia
f v u 50 25
(ii) Astigmatism
= - 1 + 2 = + 1 cm-1 (iii) Bifocal lenses
50 50 (iv) Far sightedness.
(b) Describe with a ray diagram how a person with
P = 1 = 100 + 2D
f 50 myopia can be helped by spectacles.
d.
Ans : [CBSE 2006]
(a) (i) Myopia is a kind of defect in human eye due
to which a person can see near by objects
clearly but unable to see the distant objects.
Myopia is due to (i) excessive curvature of
cornea (ii) elongation of eye ball.
(ii) Astigmatism is a kind of human eye defect in
which he cannot see simultaneously horizontal
and vertical lines both. This defect arises
either when the cornea or the eye lens or both
are not perfectly spherical. It can be corrected
by using cylindrical lenses.
(iii) Bifocal lenses with the ageing a person
may suffer myopia and hypermetropia. For
83. (a) What is dispersion of white light? What is the correction of these defects he is advised to
cause of such dispersion? Draw a diagram, to show use bifocal lenses whose upper half is concave
the dispersion of white light by a glass prism. and lower part is convex to see distant and
(b) A glass prism is able to produce a spectrum when reading purposes respectively.
white light passes through it but a glass slab does (iv) Far sightedness, a person suffering from this
not produce any spectrum. Explain why it is so. defect can see distant objects but unable to
Ans : [CBSE 2009] see nearby objects clearly. The image of an
objects is formed beyond the retina. Such
(a) Dispersion : When white light is passed through a
defects can be corrected by using a convex
prism it splits into its constituent colours splitting
lens.
of white light into its constituent colours is known
(b) A person with myopic eye may be advice to use a
as dispersion.
concave lens of suitable power/ focal length.
Light of all wavelengths in vacuum travel with
the same speed but have the different speeds in a
medium due to different refractive light of indices
for them. As a result different wavelength, deviate
at different angle. Red colour deviates least when
as violet colour deviates most.
(b) In glass slab also, dispersion takes place at AB
surface, but these splitted colours emerge out
in the form of a parallel beam which becomes
white. A glass slab whose focus are parallel can
be considered as comprising two prisms of same
refractive angle. The second identical prism can
be considered in an inverted position w.r.t. first
prism. When a beam of white light passes from one
prism it get dispersed, but on passing through the
second inverted prism, the spectrum recombine to
form a white light.

85. (a) State two main causes of a person developing near

sightedness. With the 3 help of a ray diagram,
suggest how he can be helped to overcome this
 disability? the lens he should use.
(b) The far point of a myopic person is 150 cm in Ans : [All India 2015]
front of the eye. Calculate the focal length and
The person should wear a concave lens. For myopic
power of a lens required to enable him to see
eye u = 3, v =- 40
distant objects clearly.
Ans : [CBSE 2004] 1 =1-1
f v u
a. Elongation of eye ball, and excessive curvature of
1 = 1 - 1
cornea. He may be adviced .to use a concave lens f - 40 3
of suitable focal–length.
1 =- 1
f 40

P = 100 =- 100 = - 2.5D

f ^cmh 40

89. The far point of a myopic person is 150 cm in front

of the eye. Calculate the focal length and the power
of a lens required to enable him to see distant objects
clearly.
Ans : [CBSE 2014]
For myopic person
b. f = - 150 cm u = 3, v =- 150 cm
f =?
P = 1 = 100 =- 0.66 D
f - 150
From lens formula 1 = 1 - 1
f v u
86. A person with a defective eye-vision is unable to see
= 1 - 1 =- 1
the objects nearer than 1.5 m. He wants to read books - 150 3 150
at a distance of 30 cm. Find the nature, focal length
and power of the lens he needs in his spectacles. P = 100 = - 100 = - 0.66 D
f ^cmh 150
Ans : [CBSE 2016]
= - 0.66 D
Defect is hypermetropia
v = - 1.5 m or - 150 cm, u = - 30 cm 90. A person needs a lens of power –0.5 dioptre for
1-1 = 1 correcting his distant vision he needs a lens of power
v u f +1.5 dioptre for correcting his near vision. What is
the focal length of the lens required for correcting his
1 = 1 - 1
f - 150 - 30 (i) distant vision, (ii) near vision?
Ans : [CBSE 2011]
=- 1 + 1 = - 1 + 5 i. For correcting his distant vision.
150 30 150
P = - 0. 5 D
f =+ 150 =+ 37.5 cm
4
f = 1 = 1 = - 2.0 m
A convex lens of focal length 37.5 cm is required P - 0.5
ii. For correcting his near vision
Power = 100 = 100 =+ 2.67 D
f ^cmh 37.5
f = 1 = 1 = + 0.67 m
P + 1. 5
87. The far point of a myopic person is 80 cm in front of WWW.CBSE.ONLINE
the eyes. What is the nature and power of the lens
required to enable him to see very distant objects
distinctly?
Ans : [CBSE 2016]
Concave lens is used for myopic eye for point x = 80
cm.
For viewing fat distant object, focal length of lens.
f =- x =- 80 cm
P = 100 = 100 D
f ^cmh - 80
=- 1.25 D

88. Far point of a myopic person is 40 cm. What type of

lens, should he wear so as to see the distant objects
clearly? Calculate the focal length and the power of
Chap 6 : Life Process www.cbse.online

CHAPTER 6
Life Process

ONE MARK QUESTIONS onwards?

Ans : [Delhi 2010]
Food is passed down to small intestine through
1. Which is the universal source of energy in all cells? sphincter muscles present in last part of stomach.
Ans : [Delhi 2017]
11. What is the stored form of carbohydrates in plants
ATP, Adenosine Tri Phosphate.
and animals respectively?
2. If no apparent work is being done by an organism, Ans : [Foreign 2009]
why does it takes food? [All India 2017] Starch and glycogen.
Ans :
12. What is the meaning of variegated leaf?
To carry out life processes, growth, reproduction and
for repair of worn out tissues. Ans : [All India 2009]
Variegated leaf means leaf with some green and some
3. Which pathway is common to both aerobic and non-green part.
anaerobic respiration? [All India 2012]
Ans : 13. Define the term ‘ translocation’. [Delhi 2008]
Glycolysis. Ans :
Transport of food from leaves to other parts of the
4. What would be the consequences of deficiency of plant is called translocation.
haemoglobin in our bodies? [Foreign 2012]
Ans :
Anaemia.

5. How does nutrition in a fungus different from that in

a tapeworm? [CBSE 2011 C]
Ans :
Fungus derives its nutrition either by parasitic or
saprophytic manner while tapeworm is only parasitic.

6. Name mode of nutrition in the following organisms:

(a) Fungi (b) Amoeba
Ans : [All India 2011]
a. Fungi - saprophytic
b. Amoeba — animal like nutrition 14. Why is respiration considered an exothermic process?
7. What is peristalsis? [Delhi 2011] Ans : [All India 2008]
Ans : Respiration is considered an exothermic process due
to breaking down of glucose/food in the presence of
Contraction and expansion of alimentary canal to
oxygen with release of energy.
push the food forward is called peristalsis.
15. What is breathing? [All India 2008]
8. What is the role of cartilaginous rings on trachea?
Ans :
Ans : [All India 2010]
The mechanism by which organisms intake oxygen
They prevent the collapsing of trachea when there is
from the environment and release carbon dioxide is
no air present in it.
called breathing.
9. Name the type of blood vessels, which carry blood
16. Mention two ways in which food gets oxidized in
from organs to the heart.
organisms. [CBSE 2008C]
Ans : [All India 2010]
Ans :
Veins.
Aerobic respiration and anaerobic respiration.
10. How is the passage of food regulated from stomach
17. What role do digestive enzymes play in the alimentary Saprophytic Parasitic Nutrition
canal? [CBSE 2008C] Nutrition
Ans :
1. Taking dead decay Living on or inside other
Digestive enzymes break down complex molecules of organic matter in organisms and deriving
food into simpler ones so that they can be absorbed the form of food is their food from them
by blood. called saprophytic without killing them.
nutrition.
18. Which enzyme is present in human saliva?
Ans : [Foreign 2008] 2. It shows It has intracellular
extracellular digestion.
Salivary amylase or ptyalin. digestion.
19. What are the end products of photosynthesis? 3. It does not depend It causes harm to the
Ans : [All India 2008] on living host. organism.
Glucose, oxygen and water.
4. E.g., fungi and E.g., lice, tapeworm,
20. Give two examples of variegated leaves. bacteria. leech.
Ans : [Delhi 2008]
24. How do plants exchange gases?
Crotons, money plant.
Ans : [Foreign 2017]
Plants exchange gases through stomata. Large
TWO MARKS QUESTIONS intercellular spaces ensure that each cell is in contact
with air. Carbon dioxide and oxygen are exchanged
here.
21. What is Lymph? How is it different from blood?
Ans : [All India 2018] 25. List two factors which decide direction of diffusion of
Lymph is the light yellow fluid containing lymphocyte, oxygen and carbon dioxide.
which fights against infections. Ans : [All India 2017]
Blood Lymph Environmental conditions and requirement of the
plants decide direction of diffusion of oxygen and
1. Blood is pumped Lymph is moved along carbon dioxide.
throughout the body through the normal
by heart. function of the body. 26. What are the strategies of plants to get rid of their
2. Blood transports Lymph removes waste wastes?
oxygen throughout the from the system. Ans : [All India 2017]
body. a. They throw away oxygen and water vapour
3. Blood flows through The movement of through stomata.
the body in a circular lymph is in a single b. Some wastes like gums, oil and resins may be
motion. direction. stored in old xylem or wood in stem.
c. Some wastes may be stored in leaves and bark and
4. Blood contains red Lymph is a light
shed off from time to time.
blood cells, white yellow and clear
d. Roots can also throw some wastes.
blood cells and liquid.
platelets. 27. How is respiration different in plants and animals?
5. We can see blood with Lymph cannot be seen Ans : [All India 20171
the naked eyes. with the naked eyes.
Respiration in Respiration in
6. The kidney purify the Lymph is purified in Plants Animals
blood. the nodes itself.
1. It occurs through It occurs through
22. How are fats digested in our bodies? Where does this stomata, lenticels, lungs.
process take place? [Delhi 2017] root, etc.
Ans : 2. It occurs through Animals release CO2
Fats are first emulsified with the help of bile salts stomata, lenticels, as waste into the
followed by their breakdown in fatty acids and glycerol root, etc. atmosphere.
due to the action of lipase. All these events take place 3. Plants produce glucose Animals get glucose
in first part of small intestine-duodenum. and oxygen on their and oxygen from
Saprophytic own-to carry out outside to carry out
respiration. respiration.
23. Differentiate between saprophytic nutrition and
parasitic nutrition based on the type of food and 28. Why do we feel pain or cramps in muscles after a
manner of obtaining it. [Delhi 2017] vigorous exercise? [All India 2017]
Ans : Ans :
 Actively metabolizing cells of an extremely active Arteries carry blood away from the heart (arteriole:
skeletal muscle, during heavy exercise, carry oxidation small arterial branch). They have thick and flexible
in the anaerobic condition inside the muscle cell, we feel walls to endure higher pressure of blood.
pain after a vigorous exercise because of production of Veins transport blood toward the heart (venue:
ATP by anaerobic respiration in leg muscles. small vessel that carries blood from capillaries to
29. List two ways in which plants can get rid of the veins). They have thinner wall but there are valves in
wastes. them at regular distance to prevent back flow of blood
especially when blood is returning back to heart from
Ans : [All India 2016]
lower organs.
They can throw gases and excess water through
stomata through diffusion. They can store wastes like
gums and resins in old xylem tissue (wood).

30. What is the role of acid and mucus in stomach?

Ans : [Delhi 2016]
It kills germs in food and provides acidic medium for
the action of pepsin enzyme to digest the proteins in
stomach.
Mucus protects the wall of stomach from the action of
acid and pepsin.

31. Which digestive secretion does not contain any enzyme

but is important? Discuss. [All India 2016]
Ans :
Bile juice from liver. It contains bile salts which are 37. Differentiate between respiration and breathing.
necessary for emulsification of fats. It means breaking Ans : [All India 2015]
down large fat drops to very fine droplets so that
lipase can act upon them easily. Respiration Breathing
1. It is a biochemical It is a physical process.
32. Differentiate between auricles and ventricles. process.
Ans : [CBSE 2016 C]
2. O2 reacts with Only exchange of gases.
Auricle Ventricle food and energy is
released.
1. Upper thin walled Lower thick walled
chambers. chambers. 3. Energy is released. No energy released.

2. Receive blood from Receive blood from 4. It occurs in Occur in respiratory

veins. the auricles cytoplasm and organs.
mitochondna.
3. Push blood into the Push blood into the
ventricles. arteries. 38. Write a balanced equation for photosynthesis.
Ans : [All India 2014]
33. What is the role of valves in veins?
Light
Ans : [Foreign 2016] 6CO2 + 12H2 O Chlorophyll
C6 H12 O6 + 6H2 O + 6O2
They prevent the back flow of blood especially when it 39. Name the enzyme present in Saliva? What is its
moves against gravity and under low blood pressure. role?
34. How is the small intestine designed to absorb digested
Ans : [All India 2014]
food? [All India 2016] Salivary amylase enzyme present in saliva. It breaks
Ans : down starch to sugar maltose.
Walls of small intestine has finger like projection called 40. How does nutrition take place in Amoeba? How is it
villi to increase surface area. The food is absorbed different in Paramoecium? [All India 2014]
by villi and brought into blood. Fat is brought into Ans :
lymph vessel.
Nutrition in amoeba: It occurs through phagocytosis.
35. Why are arteries thick walled and elastic? It capture food by pseudopodia (ingestion) ingested
Ans : [All India 2015] food, enclosed in cell membrane is called food vacuole.
The food is broken with enzymes present in cytoplasm
Arteries receive the blood pumped by heart with lots
and undigested food ‘is thrown out through cell
of pressure hence to tolerate and sustain this pressure
membrane.
they are thick walled and elastic.
Nutrition in Paramoecium: The cell has a definite
36. Differentiate between Artery and Veins. shape and food is taken in at a specific spot. Food is
moved to this spot by the movement of cilia present
Ans : [CBSE 2015 C]
on the entire surface of the cell.
41. Discuss how the roles of vena cava and pulmonary organisms?
veins different from each other? Ans : [Delhi 2013]
Ans : [Foreign 2014] Autotrophs can use simple inorganic molecules like
Pulmonary vein carries oxygenated blood from lungs water and carbon dioxide while complex organic
to left auricle of heart in humans. molecule are used by heterotrophic organisms as
Vena Cava collects deoxygenated blood from all proteins, fats and carbohydrates.
parts of the body and transport it to right auricle of 49. Why are ventricles thick walled and muscular?
the heart in human.
Ans : [All India 2013]
42. Why is it advisable to breathe through nose? Since ventricles have to pump blood into various
Ans : [CBSE 2014 C] organs, they are thick-walled and muscular.
There are fine hair and mucus gland in the inner lining 50. How is the length of intestine related to food habit of
of nose which filter the incoming air of germs and dust. the animal? [All India 2012]
Moreover the air attains the optimum temperature
Ans :
before reaching the lungs.
Intestine where digestion and absorption occur is
43. Define transpiration. How does transpiration help in very long in herbivores and shorter in carnivores as
upward movement of water from roots to leaves? . digesting meat is easier than digesting grass.
Ans : [All India 2014]
51. Differentiate between Photosynthesis and
Transpiration is the process of removal of water Respiration.
vapours from the aerial parts of a plant, mainly
Ans : [All India 2011]
through stomata in the leaves.
Evaporation of water molecules from the cells of Respiration Photosynthesis
a leaf creates a suction force which pulls water from 1. It occurs in all living It occurs in only
the xylem cells. This transpiration helps in upward cells. autotrophs.
movement of water from roots to leaves.
2. O2 reacts with food CO2 and H2O combine
44. Describe the structure of the human heart briefly. and energy is released. to form starch and
Ans : [Sample Paper 2014-15] water in the presence
of light.
Human heart is four chambered. The two upper
chambers are called atria and they receive blood from 3. It occurs in cytoplasm Occur in plastid-
large veins while the two lower chambers are called and mitochondria. chloroplast
ventricles. Between left atrium and left ventricle as
well as between right atrium and right ventricle are 52. Differentiate between alveoli of lungs and nephrons of
valve which allow blood to flow only from atrium to kidneys. [Sample Paper 2009]
ventricle. Ans :

45. Name the respiratory pigment in human beings? What Alveoli in the Nephrons in the
is its role? [All India 2013] Lungs Kidneys
Ans : 1. Thin walled, sac Thin walled,
Respiratory pigment, haemoglobin is present in red like structure, tubular structure,
blood cells. Haemoglobin has affinity for O2 thus surrounded surrounded
helping in its transport. with network of with network of
capillaries. capillaries.
46. What are enzyme? Do they play some role in our
2. Helps in exchange of Helps in filtration of
digestive system too?
gases between blood wastes like urea and
Ans : [CBSE 2013 C] and outside air, that uric acid from blood
They are chemically proteinaceous biocatalyst, which is, removal of CO2
increase or decrease the rate of a biochemical reaction. and taking in of 09.
The enzyme present in our digestive system 3. Waste produced is Waste produced is
help to breakdown of complex molecules of food into C02 and water vapor urine-salts, urea, uric
simpler ones. (gaseous waste) acid etc. dissolved in
water liquid waste
47. What is the role of large intestine? [All India 2013]
Ans : 53. What the components of transport system are in
highly organize plants? [All India 2017]
Water re-absorption occurs through villi, undigested
or
food is stored in rectum and thrown out through anus.
Exit is regulated by anal sphincter. 54. What is the difference between Xylem and Phloem?

48. What are the outside raw materials used by an

Ans : [Delhi 2009]
There are two conducting tissues in transport system
 of plants, first is xylem and second is phloem. in desert plants they open at night to reduce the loss
of water. Water is absorbed by roots from the soil
Xylem Phloem
along with other materials like nitrogen, phosphorus,
1. Water and mineral Transportation of iron and magnesium.
from the roots to food and nutrients
aerial parts of the from leaves to growing 61. How do autotrophs obtain CO2 and N2 to make their
plant. parts of plant. food?
This movement of Ans : [All India 2008]
substance is called
CO2 from environment/atmosphere through diffusion/
translocation.
stomata. Nitrogen from soil/environment in inorganic
2. Its movement is Its movement is (nitrates) or organic form.
unidirectional - moves bidirectional - moves
up the plant’s stem. up and down 62. Write one function each of the following components
of the transport system in human beings
3. Tracheids, vessels are Sieve tubes, blood vessels
the elements of xylem. companion cells are blood platelets
the element of phloem. Lymph
55. What is respiration? What is its importance for an
Heart
organism. Ans : [All India 2008]
Ans : [CBSE 2009 C] a. Blood vessels: transport of blood.
The breakdown of food in cells to release energy. b. Blood platelets: clotting of blood preventing its
All kind of food is broken down through oxidation- loss/leakage.
reduction reaction and its chemical energy is converted c. Lymph: carries digested fats/protects from
into a universal source of chemical energy - ATP, infection/exchange of materials between tissues
Adenosine Tri Phosphate. and blood/drains excessive fluid back to blood.
d. Heart: pumps blood to all parts.
56. What is residual volume in our lungs? What is its
importance? [All India 2011] THREE MARKS QUESTIONS
Ans :
Residual volume is the amount of air which is always
left inside the lungs in spite of forceful exhalation. It 63. What is sequence of steps in photosynthesis? How is
helps in continuous gas exchange during exhalation or it different in desert plants and those in temperate
inhalation. regions?
Ans : [All India 2018, Delhi 2017, Foreign 2015]
57. Show direction of flow of lymph with the help of flow
Chloroplast (chlorophyll), on exposure to light energy,
diagram. [All India 2010]
becomes activated by absorbing light energy, and splits
Ans : water (photolysis of water) to oxygen and hydrogen.
Lymph " tissue " sinus " lymph vessel " vein " Hydrogen reduces CO2, and synthesizes glucose.
heart. In plants of temperate regions, stomata open
during day to take in CO2 and release O2.
58. What is the role of saliva in digestion of food?
Ans : [Delhi 2017] Desert plants open stomata at night to check
excessive loss of water hence sequence of steps of
Saliva lubricates and softens the food so that it can photosynthesis are slightly different.
be easily chewed and swallowed. It contains enzyme
amylase which breaks down starch to maltose. These plants take up carbon dioxide at night and
prepare an intermediate which is acted upon by the
59. Why rate of breathing in aquatic animals has to be energy absorbed by the chlorophyll during the day.
faster than that in terrestrial animals?[CBSE 2008 C]
64. Design an activity to show that CO2 is produced
Ans :
during breathing. [Delhi 2017]
Amount of O2 dissolved in water is less than O2 Ans :
present in air therefore rate of breathing in aquatic
animals has to be faster than that in terrestrial Materials Required:
animals. Terrestrial organism need not spend so much Two test tubes, a cork with two holes, two glass tubes
energy to obtain oxygen. bent at right angle, syringe, lime water Ca(OH)2.
Procedure :
60. What are the raw materials for photosynthesis. How a. Take some freshly prepared lime water, Ca(OH)2
are they obtained by a plant? [CBSE 2008 C] in two test tubes,
Ans : b. Fit cork with two holes in test tubes A and B.
c. Fix two glass tubes in this cork of test tube A as
CO2 and water are needed for the photosynthesis. CO2
shown in the figure.
enters the leaf through stoma present on its surface.
d. Exhale air into the tube and record your
These pores open in day time in most of plants though
observations.
 e. Pass air by the syringe through the lime water (ii) Osmoregulation - The process of maintaining
contained in test tube B and record your the right amount of water and proper ionic
observations. balance in body. It is done by controlling
the amount of water and salts reabsorbed by
nephron - tubules.

(A)
Air being exhaled into lime water

67. a. How is oxygen and carbon dioxide exchanged

between blood and tissue? How are the gases
transported in human being?
b. What is haemoglobin? [CBSE 2016-17]
Ans :
a. Exchange of gases in tissues occurs through
diffusion. Oxygen is carried as oxyhaemoglobin
from lungs to tissues. It dissociates and carbon
dioxide diffuses out into blood from tissues. It is
(B) transported in dissolved form and reaches lungs
Air being passed into lime water with a syringe where again it diffuses to alveoli.
b. Respiratory pigment: Haemoglobin is a red
Observation: coloured protein present in red blood cells.
Lime water turns milky sooner in test tube A than in Haemoglobin has affinity for O2.
test tube B.
Conclusion 68. What are the important features of all respiratory
a. The exhaled air contains lot of CO2 which turns structures in animals?
lime water milky. or
b. This proves that CO2 gas is exhaled out by How are alveoli designed to maximize the exchange of
humans during respiration. gases? [Delhi 2016]
Ans :
65. What is the composition of urine? Are glucose and
All respiratory system have some important features.
proteins normally present in urine? Why? How is
a. Large surface area.
volume of urine regulated? [All India 2017]
b. Thin and delicate surface for diffusion and
Ans : exchange of gases. It is generally located in
The urine contains mainly water, various salts, urea protected inner part of body.
and uric acid. No, they are not present in urine as c. Rich blood supply to respiratory organ. Since all
glucose is reabsorbed by nephron while protein are not of them are present in alveoli hence it is perfectly
filtered from blood in glomerulus in a healthy kidney. designed for exchange of gases.
Volume of urine is regulated by
a. The amount of excess water. 69. What is excretion? Name some parts in our body
b. The amount of dissolved waste in blood. involved in this life process? [Delhi 2016]
Ans :
66. a. What is the role of mucus in stomach?
Excretion means throwing out metabolic waste from
b. What are the two vital functions of human
living body. Many organs perform this process such as
kidney?
a. Kidneys remove nitrogenous wastes like urea and
Ans : [Foreign 2017] uric acid in urine.
a. To protect the stomach lining from the action of b. Sweat and oil by glands in skin.
acid and pepsin. c. Carbon dioxide and water vapor by lungs.
b. The two vital functions of human kidney are: d. Faces or undigested food by large intestine.
(i) Excretion - Removal of toxic wastes like urea, e. Bile pigments by liver. It also converts toxic
uric acid. ammonia to urea.
70. What is the need to have a transport system in d. Enzymes produced in intestinal juice complete
complex organisms? [CBSE 2013C] the digestive process.
Ans : e. Digested food - amino acids, sugar are absorbed
by the blood capillaries present in the villi of
The transport system of an animal moves substances
intestine.
to where they are needed in the body. Even the
f. Digested fats are absorbed by lymph vessels
smallest animal must have the means of transporting
present in the villi of intestine.
substances around its body. Oxygen and food molecules
must move to all the cells, and the waste products 74. Give schematic representation of different pathways of
must be removed from the cells and expelled into the breakdown of glucose molecule.
environment. It occurs through diffusion mainly. [All India 2010,2014,2016]
In a multicellular organism, all cells are not in Ans :
contact with the surrounding hence diffusion will be
insufficient for it. A variety of fluid systems, called
vascular systems, help such transport in most members
of the animal kingdom.

71. Explain how the air is inhaled during breathing in

humans. [Delhi 2012] 75. Which process in plants is responsible for clouds
Ans : formation and precipitation? Define the process. How
is this process important for the plants?
Mechanism of inhalation:
Ans : [All India 2010]
a. The diaphragm and rib muscles contract which
make the throat move upwards and outwards. They are due to transpiration. Transpiration is
b. The volume inside the thoracic cavity increases evaporation of water from aerial parts, leaves of plant,
i.e., it expands. through mainly stomata.
c. Air pressure inside the thoracic cavity decreases. a. In plants, water rises because of transpiration and
Thus, air from outside rushes into the lungs / in nature water cycle operates because of it.
alveoli through nostrils, trachea and bronchi. b. Transpiration is the process of cooling the parts
of a plant.
72. How is food transported in a plant? c. Evaporation of water molecules from the cells of
Ans : [Foreign 2011] a leaf creates a suction force which pulls water
The food prepared by plant may be sucrose, amino from the xylem cells. This transpiration helps in
acids or other materials. It is done with the help of upward movement of water from roots to leaves.
living cells- sieve tubes and companion cell of phloem 76. What is the fate of glucose molecule in
tissue by utilizing energy of ATP. The movement a. Anaerobic respiration in Yeast and lactobacillus
occurs both upwards and down ward from the place bacteria?
of formation (leaves) to storage organ (roots or stems) b. Aerobic respiration in human cells.
from storage organ to organ of its utilization (growing Write chemical equation for each type.
buds) depending upon the situation. or
a. Translocation: Transport of organic food from the What are the different ways in which glucose is
leaves to the other parts of the plants through the oxidized to provide energy in various organisms?
sieve tubes of phloem tissue is called translocation. [All India 2010, 2013, 2015]
b. Importance: It is an essential process as every part
Ans :
of the plant requires food. For energy, building
and maintenance. Pyruvate (3 carbon molecule) is formed by glucose
c. Sugars are synthesized in the leaves whereas (6 carbon molecule) through Glycolysis in all
hormones are synthesized in the growing parts of the organisms. Anaerobic Respiration: Anaerobic
roots and shoots. respiration in microbe such as yeast which is also
known as fermentation produce end-products as
73. What are the main events occurring in the small follows:
intestine? C6H12O6 $ Pyruvate
Fermentation

Ans : [All India 2011] Glucose Ethyl alcohol2C H OH + 2CO + Energy

2 5 2
Carbon dioxide
The main events occurring in the small intestine are
as follows: Aerobic respiration:
a. Bile emulsifies fat present in the food The second step of respiration in human cell takes
(emulsification means breaking of fat molecules place in the presence of oxygen inside mitochondria
into smaller globules). and is, therefore, called aerobic (in air) respiration.
b. Pancreatic juice containing trypsin for digesting During this stage, the end product of glycolysis, the
proteins and pancreatic amylase for starch act 2 molecules of pyruvic acid enter the mitochondria
upon the food. of aerobic cells and undergo complete oxidation
c. Bicarbonate ions secreted by duodenal wall make by enzymes in Krebs cycle into CO2 and H2O and
the medium alkaline because it is required for the release large amount of energy (30 ATP molecules).
action of pancreatic enzynies. Thus, complete oxidation of one molecule of glucose
 and aerobic respiration generates in total of 38 ATP pulling water and minerals upward through xylem
molecules. elements-ascent of sap. Thus transpiration helps
Presence of Oxygen
Glucose $ Pyruvate in upward movement of water from roots to leaves.
Carbon dioxide + Water + Energy 7. The roots of a plant absorb water and dissolved
substances from the soil, which is needed by the
77. Leaves of a healthy potted plant were coated with aerial parts of the plants. As such these substances
Vaseline to block the stomata. Will this plant remain are to be transported from roots up to stem,
healthy for long? Stage three reasons for your leaves and flowers.
answer. [All India 2009]
Ans : 80. Describe the mechanism of gaseous exchange in tissues
and lungs. [Delhi 2015]
No, the plant will not stay healthy for a long time. or
The reasons are: How is oxygen and carbon dioxide transported in
a. It will not be able to exchange O2 and CO2, hence human being? [CBSE 2016]
respiration will be affected adversely. or
b. Photosynthesis will also be affected as CO2 will How is oxygen and carbon dioxide transported in
not be available. human being? Explain clearly how the air is inhaled
c. Transpiration will not take place hence there will and exhaled during breathing in humans.
be no ascent of sap, hence no water absorption
Ans : [All India 2009]
from the soil.
Exchange of gases in tissues:
78. If a plant is kept covered with a polythene sheet, a. Most of oxygen is carried by haemoglobin in
we notice some water drops on the inner side of the blood. On reaching the tissues, it gets diffused
sheet after some time. What are they due to? Name into the cells as it is in higher concentration than
and define the process. What is the significance of in the cells.
this process in plants and in nature? How does b. The carbon dioxide, which is formed in the cells,
transpiration help in upward movement of water from gets accumulated there in higher concentration
roots to leaves? [Delhi 2015] as compared in the blood, now diffused into the
Ans : blood.
c. The CO2 mostly dissolved in blood plasma reaches
If a plant is kept covered with a polythene sheet, we
the lungs, from where it is expelled out during
notice some water drops on the inner side of the sheet
exhalation.
after sometime due to transpiration. The loss of water
Mechanism of Inhalation:
in the form of vapour from the aerial parts of the
The thoracic cavity expands when diaphragm and
plant is known as transpiration. This process helps in
rib muscles contract. The thorax moves upwards
the absorption and upward movement of water and
and outwards, increasing the volume inside thoracic
minerals dissolved in it from roots to the leaves. It
cavity. The air pressure in the cavity decreases, hence
also helps in temperature regulation.
the air rushes into the lungs through nostrils, trachea
and bronchi.
FIVE MARKS QUESTIONS Mechanism of Exhalation :
Exchange of gases between alveolar sacs and blood
occurs and air having CO2 enters the alveoli. The
79. How are water and minerals absorbed and transported thoracic cavity comes back to its original size as
in the plants? [All India 2009] diaphragm muscles relax. Air containing CO2 is
Ans : exhaled out through bronchi, trachea and nostrils.
1. Transpiration is the process of removal of water
vapors from the aerial parts of a plant, mainly
through stomata in the leaves.
2. There are two conducting tissues of plants: first
is xylem and second is phloem. Tracheids and
vessels which are two kinds of elements of xylem.
3. Tracheids are found in all vascular plants. They
are spindle shaped, have only pits and are not
very efficient.
4. Vessels are found in flowering plants, are tube
like, have perforation plates and pits making them
more efficient.
5. When loss of water in vapour occur from leaves
of plants due to transpiration, deficit of water
is created in the leaves. Evaporation of water
molecules from the cells of a leaf creates a suction 81. What are the differences between Aerobic and
force which pulls water from the xylem cells. Anaerobic respiration? Name some organisms which
6. Water and minerals dissolved in it move up to use the anaerobic mode of respiration.
leaves from root through tracheids and vessels, Ans : [All India 2008]
 Aerobic Anaerobic 84. a. What are two vital functions of the human kidney?
respiration respiration b. Draw labelled diagram of human urinary system.
Ans : [Delhi 2017]
1. Presence of air Presence of air not
required. required a. The two vital functions of kidney are —
1. Excretion of nitrogenous wastes.
2. Occur in two steps: Complete process 2. Osmoregulation - regulation of water and salt
1st Glycolysis in occurs in cytoplasm. content in blood.
cytoplasm.
2nd in mitochondria.
3. Glucose completely Glucose incompletely
oxidized to CO, and oxidized to either an
H2O. organic acid or alcohol
with CO2.
4. Large amount of Less energy produced
energy produced
5 E.g., man, higher E.g., yeast,
plants lactobacillus
85. Describe double circulation in human beings. Name
82. a. Mention any two components of blood.
the group of animal with double circulation? How is it
b. Trace the movement of oxygenated blood in the
important for them?[Foreign 2017] [All India 2016-17]
body.
c. Write the function of valves present in between Ans :
atria and ventricles. Such a flow in which blood enters the heart twice
d. Write one structural difference between the is called double circulation. It helps in keeping the
composition of artery and veins. [All India 2018] oxygenated and deoxygenated blood separate.
Ans : The right atrium receives blood from the vena
a. plasma, blood cells. cava and pumps the blood into the right ventricle.
b. Pulmonary vein from lungs " left atrium left Blood is sent to lungs, where it is oxygenated. Then,
ventricle " aorta " arteries to all organs. it is sent through the right and left pulmonary veins to
c. Valves prevent backflow of blood from ventricles the left atrium where it is pumped to the left ventricle.
to atria when latter are contracting. The blood then travels to the ascending aorta where it
d. Arteries have thick, muscular and elastic walls. leaves the heart and delivers oxygen to different parts
Veins have thinner, less muscular walls but have of the body.
valves.

83. a. Define excretion.

b. Name the basic filtration unit present in the
kidney.
c. Draw excretory system in human beings and label
the following organs of excretory system which
perform following functions:
(i) form urine
(ii) is a long tube which collects urine from
kidney.
(iii) store urine until it is passed out.
Ans : [All India 2018]
a. Throwing out wastes from the living body.
b. Nephron.
c. (i) kidney (ii) ureter (iii) urinary bladder
Birds and mammals have double circulation because
they need to maintain a constant body temperature
(warm blooded animals or endotherms).

86. Where are kidneys located in our body? Show the

location of different parts of urinary system in man.
What is the importance of kidneys in our body?
Ans : [All India 2016]
The kidneys (renal glands) like high in the abdominal
cavity near and on both sides of the vertebral column.
The right kidney is slightly lower than the left to make
room for the liver. Each kidney is bean shaped and the
 concave portion faces medially. The kidney collects passes through the proximal convoluted tubule , Loop
and transports urine from the kidney to ureters. of Henle, the distal convoluted tubule so that useful
The kidneys regulate: substances are re-absorbed by blood present in the
a. The volume of blood plasma (blood pressure). capillaries around them.
b. The concentration of waste products in the blood
(excretion).
c. The concentration of electrolytes such as Na+, K+,
HCO3- and other ions (osmoregulation).
d. The pH of plasma.
e. Figure :

The liquid is now called urine is concentrated and

87. What are the different components of blood? Give the collected in collecting duct and poured in ureters to
function of each of them. [Foreign 2015] be carried to urinary bladder. Urine is passed out
Ans : through urethra, when the urinary bladder is full and
due to pressure there is an urge to do so. Sphincter
Blood is a liquid connective tissue. It is chiefly formed muscles regulate this process
of two components:
a. Fluid matrix or plasma: It is of pale colour Osmoregulation and excretion are intimately
and transports much substance like dissolved related, these processes together maintain homeostasis
carbon dioxide, glucose, amino acids, urea etc. (i.e. staying the same), and are performed by the
has mainly water, some proteins like albumin, same set of organs. The kidney is the major organ of
fibrinogen (blood clotting protein) and many osmoregulation and excretion in vertebrates.
other substances to be transported. 89. Usman collected her saliva and mixed it with liquid
b. Cellular elements which are of three types: A in the test tube. In another test tube she took only
(1) Red blood corpuscles (R.B.C) or erythrocyt. liquid A after about 10 minutes, she added a few
es, which transport O2 and CO2. They are drops of iodine solution to the mixture in the first test
enucleated, disc shaped, full of a red colored tube. It did not show any colour but when she treated
protein pigment, hemoglobin. the other test tube with iodine, a blue black colour
(2) White blood corpuscles (W.B.C) or leucocytes, appeared. Now answer the following questions:
which fight disease-causing agent. They are a. What is the aim of this activity?
larger, nucleated and are of different types. b. What is liquid A?
(3) Blood platelets or thrombocytes, which help c. Why did the first test tube not show any colour
in blood clotting. They are fragments of some change with iodine while the second one did?
larger cell hence do not have nucleus. d. Which enzyme is responsible for such a result?
88. Draw neat and labeled diagram of nephron and
e. Why does a piece of bread chewed for a long time
describe the process of urine formation. tastes sweet?
or Ans : [All India 2010]
Describe structure and functioning of nephron. a. To show the action of salivary amylase on starch.
Ans : [All India 2012] b. Liquid A is starch.
Within the kidney are small functional units called c. The first test tube did not show any colour
nephrons, which are made up of glomeruli, Bowman’s change with iodine because starch was not present
capsule, proximal convoluted tubule, loop of Henley1 anymore in it. It was already digested by salivary
s loop, distal convoluted loop, and collecting duct. amylase present in saliva. The colour of liquid in
Steps of urine formation: Each kidney is made of the second one changed to blue black as the starch
millions of nephron. Each nephron has a hollow cup was still unchanged due to absence of the enzyme.
like Bowman’s capsule and a long tubule system d. Salivary amylase enzyme is responsible for such
following it. Arteriole branching from renal artery a result.
make bunches of capillaries, one of which is called a e. A piece of bread chewed for a long time tastes
Glomerulus. The first step in the filtration process is sweet because the starch is broken down by
when the blood enters the Glomerulus, where it is then salivary amylase to maltose sugar.
pumped through the porous walls into the Bowman’s 90. How are oxygen and CO2 transported in human
space. This filtered plasma is mainly water, various beings? How are lungs designed to maximise the area
salts, urea and glucose. The “glomerular filtrate” then
 for exchange of gases? the dot like structures present in these cells.
Ans : [All India 2008,2016-17]
Exchange of gases in tissues occurs through diffusion.
Oxygen is carried as oxyhaemoglobin from lungs to
tissues. It dissociates and carbon dioxide diffuses out
into blood from tissues. It is transported in dissolved
form and reaches lungs where again it diffuses to
alveoli. Lungs have a tree like branching pattern Ans : [Delhi 2017]
of bronchi and bronchioles. The terminal part of
Stomata. Gas exchange and transpiration occur
bronchiole ends into sac like structures called alveoli
through the stomata. Dot like structures are called
which are present in groups. Alveoli have curved wall
chloroplasts.
to increase surface area for exchange of gases. The
wall of alveoli is extremely thin and is lined by blood 95. Name the chemical in small tube hanging in conical
capillaries. flask. Why is it being used?
91. (i) Explain the importance of the following:
(a) salivary amylase
(b) villi
(c) pepsin
(ii) Explain how oxygenated blood from this chamber
is sent to all parts of the body.
Ans : [All India 2008]
Ans : [Delhi 2017]
(i) (a) Salivary amylase: It’s an enzyme present in
the saliva, secreted by salivary glands. It Potassium hydroxide. It is used to absorb carbon
digests starch into maltose there by starting dioxide released by germinating seeds during
the digestion of carbohydrate in the buccal respiration.
cavity.
(b) Villi: They increase the surface area for 96. Identify structure 1-4 in the given figure:
absorption of digested food into the blood.
(c) Pepsin: It is a digestive enzyme secreted
by gastric glands. It is responsible for the
digestion of proteins in stomach.
(ii) When the left atrium contracts, the oxygenated
blood is poured into the left ventricle. When the
left ventricle contracts the blood is pumped into
Ans :
the aorta, the largest artery which distributes it
to all the parts of the body through arteries. 1. Guard cells 2. Vacuole 3. Stoma 4. Chloroplast.

92. In order to prepare a temporary mount of a leaf peel 97. A student set up apparatus as shown in figure. After 8
to observe stomata, which chemicals used for staining hours what is he likely to observe. Explain the reasons.
and mounting? [Delhi 2017]
Ans :
The chemicals used for staining and mounting
respectively are safranin and glycerine.

93. What are the possible observations in the given setup?

[Delhi 2017]

Ans :
a. Water would have risen in the tube as the oxygen
present in the airtight flask would have been used
up by germinating seeds for their respiration and
CO2 gas which is being produced them must
have been absorbed by KOH. As a result partial
Ans : vacuum created will make water from beaker
move up.
Nothing will happen to the level of water/ KOH as
b. Water will rise initially while seeds are germinating
vacuum will not be created in the flask.
but fall later.
94. Name the gap formed between the kidney shaped cells c. Water.
in the given figure. What role do they play? What are
Chap 10 : Light Reflaction and Refraction www.cbse.online

CHAPTER 10
Light Reflaction and Refraction

1. ONE MARK QUESTIONS convex mirror for seeing traffic at the rear?
Ans : [CBSE 2015]
Advantage of Convex Mirror: It provide wider view of
1. Write down four important characteristics of image the rear traffic.
formed by a plane mirror. Disadvantage: It does not give the correct distance of
Ans : [CBSE 2014] the vehicle at the rear.
Image is virtual, erect, laterally inverted and of same
5. What are the units of power of a lens?
size as object.
Ans : [CBSE 2015]
2. Describe a spherical mirror. If the focal length is measured in metre then the unit
Ans : [CBSE 2014] of power of a lens is dioptre.
Spherical mirror is a part of a sphere. If reflection
takes place from inside, it is said to be concave mirror,
and if the reflection takes place from outside surface
it is a convex mirror.

3. Define the following terms in relation to concave 6. Give two uses of a convex lens.
spherical mirror:
Ans : [All India 2016]
a. Pole
b. Centre of curvature Convex lens are used in (i) spectacles, (ii) telescopes,
c. Radius of curvature (iii) microscopes, (iv) camera.
d. Principal axis
e. Principal focus 7. Give one use of a concave lens.
f. Aperture Ans :
g. Focal length (each one mark) Concave lenses are used in (i) shaving mirror, (ii) flash
Ans : [CBSE2013, 2014, 2015] lights,
a. The mid point of mirror is known as pole. 8. What is a prism?
b. The centre of curvature of a spherical mirror is
Ans : [CBSE 2015,2016]
the centre of that sphere of which mirror is a part,
c. The distance between pole and centre of curvature A prism is an optical device with two triangular
is called radius of curvature of the mirror. bases along with three rectangular lateral surfaces
d. The straight line joining the pole and centre of commonly inclined at an angle of 60°.
curvature is called principal axis.
e. The point on the principal axis through which 9. Define the term reflection.
parallel rays to the principal axis passes or appear Ans : [CBSE 2016]
to pass after reflection. The bouncing back of a ray of light in the same
f. The diameter of the mirror or size of the mirror is medium after striking on a surface of an object.
called aperture.
g. The distance between focus and pole of a mirror 10. Define the terms:
is the focal length of the mirror. a. Angle of incidence
b. Angle of reflection
4. What are the advantages and disadvantages of using a c. Plane of incidence
 Ans : [CBSE 2016] TWO MARKS QUESTIONS
a. The angle between incident ray and normal at the
point of incidence is called angle of incidence +i .
19. If the image formed by a convex lens is of the same
b. The angle between the reflected ray and normal at
the point of incidence is called angle of reflection size as that of the object. What is the position and
+r . nature of the image with respect to the lens?
c. A plane containing, incident ray, normal, and Ans : [CBSE 2012, 2013]
reflected ray is known as plane of incidence. The image will be real, inverted and will be formed at
centre of curvature of the lens.
11. State the laws of reflection.
Ans : [All India 2010] 20. How can you identify the three types of mirrors
Laws of Reflection without touching them?
a. The incident ray, the reflected ray and the normal Ans : [CBSE 2011]
at the point of incidence are always in the same a. If the image formed is erect, of same size, and at
plane. equal distance behind the mirror as object and is
b. +i = +r in front of the mirror, then mirror is plane.
b. If the image is of larger size and erect and changes
12. Explain why we see the sign front of to inverted and smaller size by changing the
the some vehicles. position of mirror from the object it is concave
Ans : [CBSE 2015] mirror.
Because the image of laterally inverted written letter c. If the image is smaller and erect for all positions
will once again laterally inverted in the rear view mirror of mirror from the object, it is a convex mirror.
of the vehicle going ahead and image so produced will
21. (a) What happens to a ray of fight when it travels
be erect image of the word AMBULANCE.
from one medium to another having equal
13. What is the radius of curvature of a plane mirror? refractive indices?
Ans : [CBSE 2015] (b) State the cause of refraction of fight.
Ans : [CBSE 2011]
The radius of curvature of a plane mirror is infinite.
(a) If a ray travels from one medium to another
14. How many images are formed by two parallel mirrors? medium of same refractive indices then it will not
Ans : [CBSE 2015] bend and travels in a straight line.
(b) Change in speed of light is the cause of
The images formed by two parallel plane mirrors will
refraction. -
be infinite.
22. (a) What should be the position of the object, when a
15. Name a mirror that can give an erect and enlarged
concave mirror is to be used:
image of an object.
(i) as a shaving mirror, and
Ans : [CBSE 2011, 2012, 2013] (ii) in torches producing parallel beam of fight?
Concave mirror (b) A man standing in front of a mirror finds his
image having a very small head and legs of normal
16. The radius of curvature of a spherical mirror is 20 cm. size. What type of mirror are used in designing
What is its focal length? such a mirror?
Ans : [CBSE 2011] Ans : [CBSE 2011]
Focal length f = R = 20 = 10 cm (a) (i) Face must be placed in between the pole and
2 2
focus of the mirror so that enlarged, erect
17. Light enters from air to glass having refractive index image of face can be formed.
1.50. What is the speed of light in glass? Speed of light (ii) At focus, because rays coming from the focus
in air is 3 # 108 m/s. after reflection will become parallel.
(b) It is a combination of convex mirror (small head)
Ans : [CBSE 2011]
and plane mirror (legs of normal size).
Speed of light in glass
8 23. Name the type of lens that can be used . as magnifying
v = c = 3 # 10 = 2 # 108 m/s
n 1.5 glass. Give reason(s) and draw a ray diagram to
support your answer.
18. The refractive index of diamond is 2.42. What is the Ans : [CBSE 2011]
meaning of this statement?
A convex lens of smaller focal length can be used as
Ans : [CBSE 2011]
magnifying glass. When an object is placed in between
The meaning of refractive index of diamond is 2.42 the pole and focus of the convex lens then enlarged,
is that speed of light in diamond is 1/2.42 times the erected and same side of object image is formed.
speed of light in air/vacuum D,
i.e. speed of light in diamond
8
v = c = 3 # 10 = 1.24 # 108 m/s
n 2.42
 27. (a) Name the spherical mirror used as:
1. Shavingmirror,
2. Rearview mirror in vehicles,
3. Reflector in search – fights.
(b) Write any three differences between a real and
virtual image.
Ans : [CBSE 2012]
(a) 1. Concave mirror,
24. An object is placed at the following distances from a 2. Convex mirror,
concave mirror of focal length 15 cm. 3. Concave parabolic
(a) 10 cm (b) Differences between a real and virtual image :
(b) 20 cm
Real Image Virtual Image
(c) 30 cm
(d) 40 cm It can be taken on a It can not be taken on
Which position of the object will produce: screen a screen
(i) Virtual image It is always inverted It is always erected
(ii) A diminished real image
(iii) An enlarged real image When reflected or When reflected or
(iv) An image of same size. refracted rays actually refracted rays appear
Ans : [CBSE 2011] meet at a point, then to meet at a point
real image is formed. then virtual image is
Given, concave mirror of f= 15 cm. formed
a. When object is placed at a distance 10 cm from
mirror (between P and f) image is virtual, enlarged 28. What is meant by power of a lens? Give its SI unit.
and erected. When two or more lenses are placed in contact, what
b. For object in between 2F and 3 i.e. 40 cm image will their combined power?
is inverted, diminished and real.
c. For object in between F and C (20 cm), image is Ans : [CBSE 2012]
inverted, enlarged and real beyond 2F(C). Power of a lens is the ability of the lens to converge or
d. For object at 2F (30 cm), the image is of same diverge a ray of light incident on it. It is the reciprocal
size. of the focal length of the lens, i.e. P = 1f . The SI unit
of power is D(dioptre) if f is measured in metre.
25. (a) What is meant by refraction of fight?
(b) If on applying Cartesian sign convention for 29. For the same angle of incidence in media P, Q and
spherical lenses, the image distance obtained is R, the angles of refraction are 45°, 35° and 15°
negative, state the significance of the negative respectively. In which medium will the velocity of
sign. light be minimum? Give reason.
Ans : [CBSE 2011] Ans : [CBSE 2012]
(a) When a ray of light passes from one medium to
As n = c = sin i & v = c sin r
another it bends from its path. The phenomenon v sin r sin i
of bending a ray of light when it passes from one for same incident angle, v will be minimum for
medium to another is called refraction of light. minimum value of angle r i.e. medium R.
(b) In a lens if the image distance is negative then its
meaning is that image formed is at the same side 30. Define absolute refractive index. Absolute refractive
of object, virtual and erect. The lens is concave indices of medium A and medium B are na and nb
lens. respectively, what is the refractive index of medium
B with respect to medium A? How does the velocity
26. What is minimum number of rays required for locating of light vary with change in the optical density of the
the image formed by a concave mirror for an object? media?
Draw a ray diagram to show the formation of a virtual Ans : [CBSE 2012]
image by a concave mirror.
Absolute refractive index of a given medium, w.r.t.
Ans : [CBSE 2011]
air/vacuum is known as absolute refractive index of
We require minimum two rays for locating the image the medium
formed by a concave Speed of light in vacuum or air
n =
Speed of light in medium

n = c as c > v
v
n >1
b n = Velocity of light in B = vb = na
a
Velocity of light in A va nb
Higher the optical density, lesser is the velocity of
light in the medium
31. As the velocity of light increases, the refractive index Ans : [CBSE 2014]
of the medium decreases. Light enters from air to water When a ray passes from optically rarer to denser
having refractive index 4/3. Find the speed of light in medium it bends towards the normal.
water. The speed of light in vacuum is 3 # 108 m/s.
na = 1.36 alcohol
Ans : [CBSE 2012]

Given: a n = 4 , c = 3 # 108 m/s

w 3
a
w v =?
As an = c & v = c
w vw wn
a

8
vw = 3 # 10 # 3
4
= 2.25 # 108 ms-1

32. What is meant by radius of curvature of a spherical a. nh = 1.44 kerosene oil

mirror? How is it related to the focal length of the nt = 1.47 turpentine oil
mirror? b. 1.44
Ans : [CBSE 2013]
Radius of curvature of a spherical mirror is the radius
of the sphere of which mirror is a part. It is the distance
between pole and centre of curvature of a mirror.
The radius of curvature is equal to the twice the focal
length
R = 2f

34. With the help of ray diagram show that angle of

incidence is equal to the angle of reflection when a ray
is incident on the concave/convex mirror.
Ans : [CBSE 2014]

33. Refractive index of turpentine oil, kerosene and alcohol

are 1.47, 1.44 and 1.36 respectively. On the basis of
this information, complete the following ray diagram
to show path of ray of light through each medium.
Give reason for your answer.

35. A doctor has prescribed a corrective lens of power +1.5

D. Find the focal length of the lens. Is the prescribed
lens diverging or converging?
Ans : [CBSE 2011]

f = 1 m = 1 m = + 10 m
P + 1.5 15

=+ 2 m
3
 f =+ 66.7 cm 40. An object is placed at the focus of a convex lens. Draw
+ f means the lens is convex (converging) lens. a ray diagram to locate the position of the image
formed, if any. State its position and nature.
36. With the help of a ray diagram, show that the
Ans :
formation of the image of an object by a concave
mirror when it is placed at the centre of curvature. Image is formed at 3, image will be real, inverted
Ans : [CBSE 2012] and enlarged.

37. Draw a ray diagram for the image formed by a concave

41. Define the term magnification. Write its formula also.
mirror when the object is placed beyond its centre of
curvature. Ans : [CBSE 2013]
Ans : [CBSE 2011] Magnification m of a mirror gives the relative extent to
which the size of image of an object is magnified w.r.t.
size of object. It is the ratio of size of image (h2 ) to size
of an object (h1 ).
Size of image
m = = h2 =- v
Size of object h1 u

42. Write the relation between object distance and image

distance from a lens and focal length of a lens.
Ans : [CBSE 2013]
38. Differentiate between reflection and refraction of light. 1 =1-1
Ans : [CBSE 2012] f v u
43. With the help of ray diagrams differentiate between a
Reflection Refraction converging lens and a diverging lens.
It is the phenomenon It is the phenomenon of Ans : [CBSE 2013]
of bouncing back of ray bending a ray of light
of light in the same when it travels from
medium after striking one another medium.
with a surface
+i = +r (angle of +i ! +r (angle of
reflection) refraction)
Reflection can take Refraction can take
place from any surface. place from a transparent
interface..

39. Define optical centre and principal axis of a lens.

Show the path of the refracted ray when a ray of light
is incident towards the optical centre of concave lens.
Ans : [CBSE 2012]
Mid point of a lens through which a ray of light passes
undeviated is known as optical centre.
A straight line joining two centre of curvatures of
the lens is called principal axis of lens.

44. If the image formed by a spherical mirror for all

positions of the object placed in front of it, is always
erected and diminished, what type of mirror is it?
Draw a labelled ray diagram to support your answer.
Ans : [CBSE 2018]
It is a convex mirror. Ray diagram for any position
 of object
47. (a) For the same angle of incidence 45°, the angle of
refraction in two transparent media; I and II is
20° and 30° respectively. Out of I and II, which
medium is optically denser and why?
(b) Light enters from air to diamond which has
refractive index of 2.42. Calculate the speed
of light in diamond, if speed of light in air is
45. State the laws of refraction of light. Explain the term 3 # 108 ms-1 .
‘absolute refractive index of a medium’ and write Ans : [All India 2011]
an expression to relate it with the speed of light in
a. For the same angle of incidence. The refracted
vacuum.
ray in medium I deviates less than in medium II.
Ans : [CBSE 2018] Hence medium I is more denser than medium II.
Laws of refraction:
a. The incident ray, refracted ray and normal to the
point of incidence all lie in the same plane.
b. The ratio of sin of incident angle to sin of angle of
refraction for a given pair of medium is constant.
sin i = constant
sin r
Absolute refractive index of a medium is the ratio
of speed of light in air or vacuum to speed of light
in the medium.
Absolute refractive index
Speed of light in air/vacuum b. Refractive index of diamond = 2.42
= Speed of light in air = 3 # 108 m/s
Speedof light in medium
Speed of light in diamond = ?
THREE MARKS QUESTIONS n =
Speed of light in air
=c
Speed of light in diamond v
8

46. A ray of light is incident obliquely on a glass slab. v = c = 3 # 10

n 2.42
Draw a ray diagram showing the path of the light ray.
Clearly, mark angle of incidence, angle of refraction, v = 1.24 # 108 m/s
angle of emergence and lateral displacement of the ray. 48. A student focused the image of a candle flame on a
Give a formula to find refractive index of glass slab in white screen by placing the flame at various distances
terms of angle of incidence and angle of refraction. from a convex lens. He noted his observations:
Ans : [All India 2011]
When a ray passes from optical rarer to denser Distance of flame Distance of screen
medium, it bends towards the normal and vice versa. from the lens (cm) from the lens (cm)
60 20
40 24
30 30
24 40
15 70
a. From the above table, find the focal length of lens
without using lens formula.
b. Which set of observations is incorrect and why?
c. In which case the size of object and image will be
same? Give reason for your answer.
Ans : [CBSE 2012]
a. In observation (iii) of the table given u = 30 cm, v =
30 cm, which is only possible when u = v = 2f(at C)
2f = 30 or f=15 cm
+i = angle of incidence
+r = angle of refraction 49. (a) Define power of a lens and write its SI unit.
(b) A convex lens forms a real and inverted image of
+e = angle of emergence a needle at a distance of 50 cm from it. Where is
d = lateral displacement. the needle placed in front of the lens, if image size
a n = sin i
is equal to the object size? Also, find the power of
g
 the lens. light passing obliquely from water to alcohol.
Ans : [CBSE 2012] (b) The absolute refractive index of diamond is 2.42
and the absolute refractive index of glass is 1.50.
a. Power of a lens is the ability of a lens to bend
Find the refractive index of diamond with respect
a ray of light incident upon it. It is equal to the
to glass.
reciprocal of the focal length of the lens.
Ans : [CBSE 2013]
P =1 a. More refractive index means more optical denser
f
If f is measured in m then unit of power is dioptre medium. Here refractive index of water is 1.33
^D h . and of alcohol is 1.36 nAl > nw .
Hence alcohol is more optical denser than water.
(b) v = + 50 cm
m =1
P =?
Since, m = 1, m = v = 1
u
or u = v = 50 cm
i.e. v and u both are at centre of curvatures
C = 2f = 50 or f = 25 cm
P =1
f
b. a n = 2.42
P = + 100 D or P =+ 4D d
25 a n = 1.50
g
g
d
n =?
an
g n = ad n # ag n = da
gn
d

gn
= 2.42 = 1.61
d 1.50
52. A 4.5 cm needle is placed 12 cm away from a convex
mirror of focal length 15 cm. Give the location of
image and magnification. Describe what happens to
the image as the needle is moved farther from the
mirror.
Ans : [All India 2014]

Given: u = - 12 cm
f = + 15 cm
h1 = 4.5 cm
50. (a) A ray of light falls normally on a face of a glass
slab. What are the values of angle of incidence v = ?, m = ?
and angle of refraction of this ray? Mirror formula,
(b) Light enters from air to a medium X. Its speed 1+1 = 1
in medium X becomes 1.5 # 108 ms-1 . Find the v u f
refractive index of medium X.
1 =1-1 = 1 - 1 = 1 + 1
Ans : [All India 2012] v f u 15 - 12 15 12
a. When a ray of light falls normally on a glass slab v = + 6.6 cm
then i = 0 , and r = 0
b. vm = 1.5 # 108 m/s m = - v =- 6.6 = 0.55
u - 12
c = 3 # 108 m/s Size of image is smaller than size of object.
We know Refractive index
53. (a) State Snell’s law of refraction.
n = c (b) When a ray of light travelling in air enters
vm
obliquely into a glass slab, it is observed that the
8
or n = 3 # 10 8 = 2 light ray emerges parallel to the incident ray but
1.5 # 10 it is shifted sideways slightly. Draw a ray diagram
n =2 to illustrate it.
Ans : [All India 2014]
51. (a) Water has refractive index 1.33 and alcohol has
refractive index 1.36. Which of the two medium (a) Snell’s law = sin i = constant
is optically denser? Give reason for your answer. sin r
Draw a ray diagram to show the path of a ray of (Refractive index of the medium)
(b)
 a concave mirror then its image moves from focus to
infinity.

56. State the laws of refraction.

Ans : [All India 2015]
Snell’s laws of refraction
a. Incident ray, refracted ray and normal to the
point of incidence lie in the same plane.
b. sin i = 1 n
sin r 2

57. (a) Define radius of curvature and focal length of a

spherical mirror and show it on a figure.
(b) Write relation between radius of curvature and
focal length of a spherical mirror.
Ans : [All India 2015]
a. Distance between pole and centre of curvature is
54. A student wants to project the image of a candle flame known as radius of curvature or the radius of the
on a screen 60 cm in front of a mirror by keeping the sphere of which mirror is a part is called radius
flame at a distance of 15 cm from its pole. of curvature.
a. Write the type of mirror he should use.
b. Find the linear magnification of the image
produced.
c. What is the distance between the object and its
image?
d. Draw a ray diagram to show the image formation
in this case.
PC =radius of curvature ^Rh
Ans : [All India 2014] b. Focal length of a mirror is half of the radius of
curvature
Given: v = - 60 cm
u = - 15 cm f =R
2
a. Since the image is real the minor is concave
58. An object of height 5 cm is placed perpendicular to
- ^- 60h
b. m =- v = =- 4 the principal axis of a concave lens of focal length
u ^- 15h 10 cm. If the distance of the object from the optical
m =- 4 centre of the lens is 20 cm, determine the position,
c. Distance between object position and image nature and size of the image formed using the lens
position = 60 - 15 = 45 cm formula.
Ans : [All India 2015]
Given, object height h =+ 5 cm for a concave lens.
u = - 20 cm, f = - 10 cm
v =?
1 =1-1
d. f v u
1 =1+1
v f u
1 = 1 + 1 =- 3
v - 10 - 20 20

v = - 20 cm = - 6.66 cm
3
Image formed is virtual, erect
m = hl = v
h u

hl = h # v = 5 # b- 20 # 1 l cm
u 3 - 20

= 5 # 1 cm = 5 cm = 1.66 cm
55. Discuss the position and nature of the image formed 3 3
by a concave mirror when the object is moved from
infinity towards the pole of the mirror. 59. If the image formed by a mirror for all positions of
Ans : [All India 2015] the object placed in front of it is always erect and
diminished, what type of mirror is it? Draw a ray
When an object is moved from 3 toward the pole of
 diagram to justify your answer. Where and why do we if image formed is real. Express it in terms of
generally use this type of mirror? relation between v and u
Ans : [All India 2015] Ans : [All India 2016]
Only in convex mirror, for all positions of the object Given f = + 10 cm, u = ?
placed in front of it is always virtual, erected and For virtual image
diminished. Hence this mirror is convex mirror.
m =+ 2
As m = v or v = 2
u u
v = 2u ...(1)
1-1 = 1 ...(2)
v u f
Substituting (1) in (2)
1 -1 = 1
2u u 10

- 1 = 1
2u 10
u = - 5 cm
For real image, f = 10 cm, m =- 2
v = - 2 , v =- 2u
Convex mirrors are used in automobiles as a rear view u
mirror because of wider field of view and formation of 1-1 = 1
erect image. v u f
1 -1 = 1
60. The nature, size and position of image of an object - 2u u 10
produced by a lens or mirror are as shown below.
Identify the lens/ mirror (X) used in each case and - 3 = 1 or u =- 15 cm
2u 10
draw the corresponding complete ray diagram, (size
of the object about half of the image). 62. One half of a convex lens is covered with a black paper.
a. Show the formation of image of an object placed
at 2Fp of such covered lens with the help of ray
diagram. Mention the position and nature of
image.
b. Draw the fay diagram for same object at same
position in front of the same lens, but now
Ans : [CBSE 2016] uncovered. Will there be any difference in the
image obtained in the two cases? Give reason for
a. Convex lens when object is in between F and C your answer.
(2F).
Ans : [Delhi 2016]
a. If the lower half of the lens is covered even then it
will form a complete real, inverted image of same
size at C2(2F2) with reduced intensity of image.

b. Concave mirror when object is in between P and F

its enlarged, erected and virtual image is formed.

b. There will be no change in the nature and position

of the object except in later case the image will
be brighter.

63. What is meant by power of a lens? Write its SI unit. A

student uses a lens of focal length 40 cm and another
of - 20 cm. Write the nature and power of each lens.
61. (a) Calculate the distance at which an object should Ans : [CBSE 2017,2018]
be placed in front of a convex lens of focal length
Power of lens is the ability of a lens to converge or
10 cm to obtain a virtual image of double its size.
diverge light rays passing through it. It is the reciprocal
(b) In the above given case, find the magnification,
 of the focal length. v = 60 cm
S.I. Unit: If focal length is measured in metre then
m = hi = v & hi = 60
unit of power of a lens is Dioptre (D) ho u 4 ^- 30h
P = 1 ^D h hi = - 8 cm
f
Power of first lens: Focal length=+40 cm. Focal length Ratio = hi /ho is approximately 2:1
is positive hence it is a convex lens.
66. (a) Define real image of an object.
P1 =+ 100 =+ 100 =+ 2.5 D (b) Name the mirror that:
f ^cmh 40 cm - can give real as well as virtual image of an
Power of second lens object.
Focal length =- 20 cm - will always give virtual image of same size of
Its focal length is negative hence it is a concave lens. an object.
- will always give virtual and diminished image
f2 =- 20 m =- 1 m of an object.
100 5
- is used by a doctor in examining teeth,
P2 = 1 = - 5D (b) With the help of a ray diagram explain the use of
f2
concave mirror as solar concentrators.
64. State the laws of refraction of light. Explain the term Ans : [All India 2011]
‘absolute refractive index of a medium’ and write a. When the reflected rays after reflection actually
an expression to relate it with the speed of light in meet at a point then real image is formed.
vacuum. b. Concave mirror
Ans : [CBSE 2017] Plane mirror
Laws of refraction: Convex mirror
a. The incident ray, refracted ray and normal to the Concave mirror
point of incidence, all lie in the same plane. c. The rays coming from the sun are parallel to
b. The ratio of sine of incident angle and sine of principal axis and will concentrate at focus after
angle of refraction for a given pair of medium is reflection.
constant.
sin i =Constant
sin r
Absolute refractive index of a medium is the ratio
of speed of light in air or vacuum and speed of
light in the medium.
Absolute refractive index
67. Name the type of mirror used in the following:
speed of life in air/vacuum a. Solar furnace
=
speed of light in medium b. Side/rear - view mirror of a vehicle.
Draw a labelled ray diagram to show the formation of
FIVE MARKS QUESTIONS image in each of the above two cases.
Which of these mirrors could also form a magnified
and virtual image of an object? Illustrate with the
65. An object of height 4.0 cm is placed at a distance of
help of a ray diagram.
30 cm from the optical centre ‘O’ of a convex lens of
focal length 20 cm. Draw a ray diagram to find the Ans : [All India 2011,2015]
position and size of the image formed. Mark optical a. Concave mirror
centre ‘O’ and principal focus ‘F’ on the diagram. Also
find the approximate ratio of size of the image to the
size of the object.
Ans : [CBSE 2018]

Ray diagram: Position of O and F

b. Convex mirror

1 =1-1 & 1 =1- 1 Concave mirror form magnified virtual image of an

f v u 20 v ^- 30h object.
1 = 1 - 1 & 1 = 3-2
v 20 30 v 60
68. (a) A thin converging lens forms a
- Real magnified image. c. f = - 12 cm
- Virtual magnified image of an object placed u = - 6 cm
in front of it.
Write the positions of the objects in each case. v =?
(b) Draw labelled ray diagrams to show the image 1 = 1+1
formation in each case. f u v
(c) How will the following be affected on cutting this 1 = -1 + 1 = -1 + 2 = 1
lens into two halves along the principal axis? v 12 6 12 12
- Focal length
v = 12 cm
- Intensity of the image formed by half lens.
Ans : [All India 2011,2015] 70. (a) Define optical centre of a spherical lens.
a. When object is placed in between F and 2F(C) (b) You are given a convex lens of focal length 30 cm.
of a converging lens it will form a real magnified Where would you place an object to get a real,
image. inverted and highly enlarged image of the object?
Draw a ray diagram showing the image formation,
(c) A concave lens has a focal length of 20 cm. At
what distance an object should be placed so that
it forms an image at 15 cm away from the lens?
Ans : [All India 2011]
a. Mid point of a lens through which a ray of light
passes undeviated.
b. At f = + 30 cm, because when object is kept at fin
case of a convex lens then its real, inverted and
highly enlarged image is formed
When object is placed in between F1 and optical
centre O of a converging lens, it will form a virtual
magnified image of the object.

b.

c. f = - 20 cm, v = - 15 cm, u = ?
c. When lens is cut along the principal axis its focal Lens formula
length remains same but intensity is reduced.
1-1 = 1
69. (a) Define principal focus of a spherical mirror.
v u f
(b) For what position of the object does a concave 1 -1 = 1
mirror form a real, inverted and diminished image - 15 u - 20
of the object? Draw the ray diagram.
(c) An object 4 cm high is placed at a distance of 6 - 1 = -1 + 1 = -3 + 4 = 1
u 20 15 60 60
cm in front of a concave mirror of focal length 12
u = - 60 cm
cm. Find the position of the image formed.
Ans : [All India 2011] 71. (a) Under what condition, a concave mirror produces
a. The point on the principal axis at which the light a virtual and magnified image? Draw a labelled
rays parallel to principal axis after reflection from ray diagram to show the formation of image in
a concave mirror actually meet or appear to come the above case. Also, state the position of object
from in convex mirror on the principal axis is to produce magnified and real image.
called principal focus. (b) A ray of light moving along principal axis is falling
b. In case of a concave mirror, when the object is on a concave mirror. Draw the path of reflected
placed beyond 2F(C) then image formed is real, ray. Also, state the values of angle of incidence
inverted and diminished. and reflection in this case.
Ans : [All India 2011]
 a. A concave mirror will produce a virtual and a glass slab, it is observed that a ray of light
magnified image of the object if placed in between undergoing refraction emerges parallel to the
F and pole of the mirror. direction of incident ray. Why does it happen so?
Explain with the help of a diagram.
Ans : [All India 2011]
a. By holding concave mirror, focus the reflected
light incident on the mirror on a sheet of paper.
The distance between paper sheet and mirror
will give the approximate value of focal length of
concave mirror.
Real and magnified image will be formed if the b. Size of image reduces
object is placed in between 2F ^C h and F in front
of a concave mirror.
b. Ray of light moving along the principal axis will
retraces it path because incident angle +i =
reflected angle +r = 0 .

72. Which lens can be used as a magnifying glass? For

which position of object does a convex lens form:
a. a virtual and erect image?
b. a real and inverted image of same size as that of
object? Draw labelled ray diagrams to show the
formation of the required image in each of the c. The opposite faces of rectangular glass slab AB
above two cases. and DC are parallel and extent of bending on
Ans : [All India 2011] opposite faces is equal and opposite+i = +e .
A convex lens of shorter focal length is used as a Hence incident ray is parallel to emergent ray.
magnifying lens (glass).
74. (a) The refractive index of diamond is 2.42. What is
a. A virtual and erect image in a convex lens is
formed when object is placed in between F and the meaning of this statement?
(b) Redraw the diagram given below in your answer
O.
book and complete the path of ray.

b. A real and inverted image of same size as that

of an object is formed by a convex lens when the
object is placed at 2F ^C h .

(c) What is the difference between virtual images

produced by concave, plane and convex mirrors?
(d) What does the negative sign in the value of
magnification produced by a mirror indicates
73. (a) Describe an activity to find the approximate value about a image?
of focal length of a concave mirror.
Ans : [All India 2012]
(b) What happens to the size of the image of an
object when it is moved gradually away from a a. The refractive index of diamond is 2.42 means
concave mirror? that speed of light in diamond is (1/2.42) times
(c) In an experiment to study refraction through the speed of light in air.
 c = 2.42 or v = c
v 2.42
iii.

b.

iv.

76. (a) Draw a ray diagram in each of the following cases

c. to show the position and nature of the image
formed when object is placed:
(i) between focus and centre of curvature of a
concave mirror.
(ii) between focus and pole of a concave mirror.
Concave Convex mirror Plane
(iii) between centre of curvature and infinity for a
mirror mirror
concave mirror.
Virtual is magnified smaller in size same size (b) (i) Give mathematical formulae for determining
image as that of magnification produced by a spherical mirror.
object (ii) What does m =- 1 signify? Identify the
d. negative magnification produced by a mirror mirror that can produce it.
mean image is real. Ans : [All India 2012]
a.
75. (a) Write one use of concave mirror as well as convex
mirror.
(b) Draw ray diagrams for the following cases when a
ray of light:
(i) passing through centre of curvature of a i.
concave mirror is incident on it.
(ii) parallel to principal axis is incident on convex
minor.
(iii) is incident at the pole of a convex mirror.
(iv) passing through focus of a concave mirror
incident on it.
ii.
Ans : [All India 2012]
a. Use of concave mirrors
(i) Head light of vehicles
(ii) Used by ENT doctors to focus the light
Use of convex mirror: Used as rear view mirrors
in vehicles.
iii.

i.

b. m =- 1
m = v =- 1
u
v =- u
(i) Size of image = Size of object
(ii) Minus sign mean that the image is real and
inverted. A concave mirror can produce it
ii. when object is kept at 2F ^C h .

77. Draw the ray diagram in each case to show the

position, nature of image formed when the object is
placed:
a. at the centre of curvature of a concave mirror
b. within focal length of a convex lens
 c. between pole and focus of concave mirror n = sin i = constant
d. in front of concave lens sin r
e. in front of convex mirror (ii) Incident ray, normal to the point of incidence
Ans : [All India 2013] and refracted ray lie in the same plane.
a. 79. (a) Explain the following terms related to spherical
lenses:
(i) Optical centre
(ii) Centres of curvature
(iii) Principal axis
(iv) Aperture
(v) Principal focus
i.
(vi) Focal length
(b) A converging lens has focal length of 12 cm.
Calculate at what distance should the object be
placed from the lens so that , it forms an image at
48 cm on the other side of the lens.
Ans : [All India 2014]
a. See the key points in the beginning of this chapter.
ii.
b. f = + 12 cm,
v = + 48 cm
u =?
Lens formula
1-1 = 1
iii. v u f
1 - 1 = 1 or 1 = 1 - 1
48 u 12 u 48 12
or u = - 16 cm

80. Draw a labelled ray diagram to locate the image of an

object formed by a convex lens of focal length 20 cm
when the object is placed 30 cm away from the lens.
Ans : [All India 2015]
iv. f = 20 cm,
u = - 30 cm
v =?
Lens formula, 1 - 1 = 1
v u f
v. 1- 1 = 1
v ^- 30h 20
78. (a) A converging lens forms a real and inverted image 1 = 1 - 1 & v = 60 cm
of an object at a distance of 100 cm from it. v 20 30
Where should an object be placed in front of the f = 20 cm
lens, so that the size of the image is twice the size
R = 40 cm,
of the object? Also, calculate the power of a lens.
(b) State laws of refraction. u = 30 cm
Object is placed in between F and C ^2F h image is
Ans : [All India 2014]
formed beyond 2F ^C h enlarged image.
(a) v =+ 100 cm
m =+ 2
m = v = 100 = 50 cm
2 2

Lens formula, 1 =1-1 = 1 - 1 = 3

f v u 100 ^- 50h 100

f = 100 cm = 1 m
3 3

P = 1 =+ 3D 81. An object is situated at 8 cm from a convex lens of

f
(b) (i) Snell’s law focal length 10 cm. Find the position and nature of
image. Draw ray diagram to illustrate the formation
 of image (not to scale). hl = 60 # 4
Ans : [All India 2015] 15
hl = 16 cm
u = - 8 cm
f = + 10 cm 83. (a) Define absolute refractive index.
(b) The path of a light ray from three different media
Lens formula, 1 - 1 = 1 A, B and C for a given angle of incidence is
v u f
shown below. Study the diagrams and answer the
1- 1 = 1 following questions:
v -8 10
1 = 1 -1
v 10 8
1 = 4 - 5 = -1
v 40 40
v =- 40 cm
Virtual, erected and magnified image

82. One half of a convex lens of focal length 10 cm is

covered with a black paper. Can such a lens produce
an image of a complete object placed at a distance of
30 cm from the lens? Draw a ray diagram to justify
your answer.
(i) Which of the three media A, B or C has
A 4 cm tall object is placed perpendicular to the
maximum optical density?
principal axis of a convex lens of focal length 20 cm.
(ii) Through which of the three media, will the
The distance of the object from the lens is 15 cm. Find
speed of light be maximum?
the nature, position and size of the image.
(iii) Will the light travelling from A to B bend
Ans : [All India 2015] towards or away from the normal?
Yes, the lens will produce a complete image but (iv) Will the refractive index of B relative to C be
brightness of image will be reduced more than unity or less than unity?
Ans : [All India 2015]
(a) Absolute refractive index of a medium is the ratio
of speed of light in air/vacuum to the speed of
light in medium.
(b) (i) Angle of refraction in medium C is minimum.
Hence medium C is maximum optical denser.
(ii) In least denser medium i.e. A the speed of
light will be maximum.
h = 4 cm (iii) Towards normal
(iv) Less than 1
u = - 15 cm
v =? 84. State the relation between object distance, image
distance and focal length of a concave or convex mirror.
f = + 20 cm A concave mirror produces two times magnified real
hl = ? image of an object at 10 cm from it. Find the position
1-1 = 1 of the image.
v u f Ans : [CBSE 2016]
1- 1 = 1 For concave or convex mirrors the relation between
v - 15 20 u, v and f is given by
1 = 1 - 1 = 3 - 4 = -1 1+1 = 1
v 20 15 60 60 mirror formula,
v u f
m =- 2
v =- 60 cm
u = - 10 cm
Virtual, erect, hl = v & hl = ^- 60h
h u 4 ^- 15h m = - v =- 2 or v = 2u =- 20 cm
u
 v = - 20 cm
1+ 1 = 1
85. (a) Write relation between u, v f for lenses and for u - 3u - 30
mirrors, where u, v f are object distance, image 2 =- 1
distance and focal length respectively. 3u 30
(b) The magnification produced by a concave mirror
is m = + 4 . Write the information about the image u = - 20 cm
given by this statement. i.e. if the object is placed at a distance of 20 cm
(c) Draw a ray diagram for the following and show in front of mirror then virtual, an erected image is
the formation of the images in case of concave produced by the concave mirror.
mirror when the object is placed:
87. A 5 cm tall object is placed perpendicular to the
(i) between the pole and focus point.
principal axis of a convex lens of focal length 20 cm.
(ii) at the centre of curvature.
The distance of the object from the lens is 30 cm.
Ans : [All India 2016] Find the
a. u, v and f reflection is given by lens formula a. position
1-1 = 1 b. nature
v u f c. size of the image formed.
1+1 = 1 Ans : [All India 2014]
Mirror formula,
v u f
Given, h = 5 cm
b. m = + 4 of a concave mirror means virtual,
enlarged image is formed behind the mirror. u = - 30 cm
f = + 20 cm
c.
v =?
a. Lens formula 1-1 = 1
v u f
i.
1- 1 = 1
v ^- 30h 20
1 = 1 - 1 = 3-2 = 1
v 20 30 60 60
v = 60 cm
b. Nature of the image is real, inverted and magnified.
ii.
c. m = h2 = v
h1 u
h2 = 60
5 - 30
86. The focal length of a concave mirror is 30 cm. Find
h2 = - 10 cm
the position of the object in front of the mirror so that
the image is three times the size of the object. 88. An object 4 cm high is placed at a distance of 27 cm in
Ans : [All India 2016] front of a convex lens of focal length 18 cm. Find the
position, nature and size of the image formed.
f = - 30 cm, m =- 3
Ans : [All India 2013]
u =?
a. For real image We have h1 = 4 cm
u = - 27 cm
m = - v =- 3
u
f = + 18 cm
v = 3u v =?
Mirror formula, 1 =1+1 1 =1-1
f v u f v u
1 = 1 +1 1 =1+ 1
^- 30h 3u u 18 v 27
- 1 = 4 or u =- 40 cm 1 = 1 - 1
30 3u v 18 27
object must be 40 cm in front of mirror to get a real
inverted image by the concave mirror. v = + 54 cm
b. For virtual image m = h2 = v
h1 u
m =- v =+ 3
u h2 = 54
4 - 27
v =- 3u
h2 = - 8
From mirror formula 1 + 1 = 1 Size of image is 8 cm, - ve sign means image is real,
u v f
 inverted and 2 times magnified. v = 10 cm

89. An object 5 cm high is kept 25 cm away from a m = - v = - 10 = 2

u - 15 3
converging lens (convex lens) of focal length 10 cm.
What is nature, position and the size of the image? 91. A point object is placed at a distance of 12 cm from a
Ans : [All India 2016] convex lens on its principal axis. Its image is formed
on the other side of the lens at a distance of 18 cm
Given: h1 = 5 cm (height of object) from the lens. Find the focal length of the lens. Is the
u = - 25 cm image magnified? Justify your answer.
f = + 10 cm Ans : [All India 2011]
v =? Here, u = - 12 cm
Lens formula v = 18 cm
1-1 = 1 f =?
v u f
1 =1-1 = 1 - 1 = 1 + 1
1- 1 = 1 f v u 18 - 12 18 12
v ^- 25h 10
1 = 1 - 1 = 5-2 = 3 = 2+3 = 5
36 36
v 10 25 50 50
f = 36 cm = 7.2 cm
v = 50 cm = 16.7 cm 5
3
m = v = 18 = - 1.5
Size of image, m = h2 = v u - 12
h1 u
m =- 1.5 means the image is magnified
h2 = 16.7
5 - 25 92. (a) Two lenses have power of (i) + 2D (ii) - 4D .
What is the nature and focal length of each lens?
h2 =- 16.7 =- 3.3 cm
5 (b) An object is kept at a distance of 100 cm for a lens
Image is real, smaller in size, inverted at a distance of of power - 4D . Calculate image distance.
16.7 cm from the lens. Ans : [All India 2012]

(a) (i) P1 = + 2D
f1 = 1 = 1 m
P1 2
f1 = 50 cm
Lens is convex lens.
(ii) P2 = - 4D
f2 = 1 = 1 m
P2 -4
f2 = - 25 cm
Lens is concave lens.
b. For the lens of power P = - 4D , we have
f = - 25 cm, u =- 100 cm
90. An object is placed 15 cm from a convex mirror of Lens formula, 1-1 = 1
v u f
radius of curvature 60 cm. Find the position of image
and its magnification. 1- 1 = 1
v ^- 100h - 25
Ans : [All India 2016]
1 =- 1 - 1 = -5
Here, u = - 15 cm v 25 100 100
R = + 60 cm v = - 20 cm
f = R =+ 30 cm 93. A 4.5 cm needle is placed 12 cm away from a convex
2
mirror of focal length 15 cm. Give the location of the
v =? image and its magnification.
m =? Ans : [All India 2016]
Mirror formula, 1 =1+1
f v u h1 = 4.5 cm, u =- 12 cm
1 =1- 1 f = + 15 cm, v = ?
30 v 15 1+1 = 1
Mirror formula,
1 = 1 + 1 = 1+2 = 3 v u f
v 30 15 30 30
 1+ 1 = 1
v - 12 15 The position of screen must be 37.5 cm from the
mirror.
1 = 9
v 60 m = h2 =- v
h1 u
v = 60 = 6.7 cm
9 h2 = ^- 37.5h
4.0 ^- 25h
m = h2 =- v
h1 u
h2 = - 37.5 # 4 =- 6 cm
25
h 2 = - 6. 7
4.5 ^- 12h Image is enlarged, inverted, real and same side of
object.
h 2 = + 6. 7 # 4. 5
12
96. The power of a lens is 2.5 dioptre. What is the focal
=+ 2.5 cm length and the type of lens?
Size of image is +2.5, virtual, erect and smaller behind Ans : [Delhi 2015]
the mirror.
P = + 2.5 D
94. A convex mirror used on an automobile has 3 m
radius of curvature. If a bus is located at 5 m from f = 1 = 100 cm
P 2.5
this mirror, find the position, nature and size of the
image. f = 40 cm
Focal length is positive hence it is a convex lens.
Ans : [All India 2016]
97. A10 cm tall object is placed perpendicular to the
We have R = + 3 m
principal axis of a convex lens of focal length 30 cm.
f = R = 1.5 m The distance of the object from the lens is 20 cm. Find
2
the (i) position, (ii) nature and (iii) size of the image
u =- 5 m formed.
Mirror formula, Ans : [All India 2014]
I +1 =1 We have h1 = 10 cm
v u f
u = - 20 cm
I + 1 = 1
v ^- 5h 1.5 f = + 30 cm
I = 1 + 1 = 1 + .3 = 1.3 v =?
v 1.5 5 1.5 1.5 1-1 = 1
Lens formula,
v u f
v = 15 = 1.15 m
13 1- 1 = 1
v - 20 30
m = h2 =- v =- 1.15 = 0.23
h1 u ^- 5h 1 = 1 - 1 = 2 - 3 = -1
i.e. image is virtual, erected and smaller in size behind v 30 20 60 60
the mirror. v = - 60 cm
95. An object, 4.0 cm in size, is placed 25.0 cm in front m = h2 = v
of a concave mirror of focal length 15.0 cm. At what h1 u
distance from the mirror should a screen be placed in h2 = - 60 = 3
order to obtain a sharp image? Find the nature and 10 - 20
the size of the image.
h2 = + 30 cm
Ans : [All India 2016] Virtual, erect, enlarged image.
We have h1 = 4.0 cm 98. Find the position, nature and size of the image of an
u = - 25 cm object 3 cm high placed at a distance of 9 cm from a
f = - 15.0 cm concave mirror of focal length 18 cm.
Ans : [All India 2004]
v =?
h2 = ? h1 = 3 cm
u = - 9 cm
From mirror formula, 1 + 1 = 1
v u f
f = - 18 cm
1+ 1 = 1
v ^- 25h - 15 v =?
Mirror formula, 1+1 = 1
1 =- 1 + 1 = - 5 + 3 = - 2 v u f
v 15 25 75 75
1+ 1 = 1
v =- 75 =- 37.5 cm v -9 - 18
2
 1 = 1 +1 = 1 v = - 30 cm
v 18 9 18
^- 30h
m = h2 = - v & h2 =-
v = 18 cm h1 u 1 ^- 15h
m = h2 =- v h2 = - 2 cm
h1 u Image is real, inverted and 2 times larger.
h2 =- 18
3 ^- 9h 101. A 2.0 cm tall object is placed perpendicular to the
principal axis of a convex lens of 1 focal length 10 cm.
h2 = 6 cm
The distance of the object from the lens is 15 cm. Find
Image is formed at a distance of 18 cm behind the
the position, nature and size of the image forms.
mirror which is erected, virtual and magnified image.
Ans : [All India 2013]
99. (a) A concave mirror produces three times enlarged
In convex lens, h1 = 2.0 cm
image of an object placed at 10 cm in front of it.
Calculate the focal length of the mirror. f = 10 cm
(b) Show the formation of the image with the help of u = - 15 cm
a ray diagram when object is placed 6 cm away
v =?
from the pole of a convex mirror.
Ans : [All India 2012] Lens formula, 1-1 = 1
v u f
(a) u =- 10 cm 1- 1 = 1
Let a real image is formed in concave mirror i.e., v ^- 15h 10

m =- v =- 3 1 = 1 - 1 = 1
u v 10 15 30
v = 3u v = 30 cm
v = 3 # 10 cm = 30 cm = h2 = v
1 =1+1 h1 u
Mirror formula,
f v u h2 = 30
1 = 1 + 1 2.0 - 15
f - 30 - 10 h2 = - 4 cm
1 =- 1 - 1 = -4
f 30 10 30 Image is real, inverted and four times enlarged.

f = - 30 = - 7.5 cm
4
(b) When u =- 6 cm from pole of a convex mirror.
For convex mirror, the image will be virtual,
erected and smaller.

100. An object 1 cm tall is placed at a distance of 15 cm

from a concave mirror of focal length 10 cm. Find the
position, size and nature of the image formed.
Ans : [All India 2013]
In concave mirror
h1 = 1 cm
u = - 15 cm
f = - 10 cm
v =?
1+1 = 1
v u f
1+ 1 = 1
v - 15 - 10
1 - 1 + 1 =- 1
v 10 15 30
Chap 13 : Magnetice Effect of Electric Current www.cbse.online

CHAPTER 13
Magnetice Effect of Electric Current

ONE MARK QUESTIONS

1. Mention the shape of the magnetic field lines around

a current carrying straight conductor.
Ans : [CBSE 2016]
The magnetic field lines around a current carrying
straight conductor are in the form of concentric
circular rings around a conductor.

5. Mention the special feature regarding shape of

magnetic field lines.
Ans : [CBSE 2015]
Magnetic field lines are continuous closed loops.

6. If field lines of a magnetic field are crossed at a point,

what does it indicate?
Ans : [CBSE 2015]
If the magnetic field lines would cross each other then
2. State the observation made by Oersted on the basis
at the same point there would be two directions of
of his experiment with current carrying conductors.
magnetic field which is not possible.
Ans : [CBSE 2016]
A magnetic field is produced near a current carrying
conductor which last so long till there is current in the
conductor on reversing the current the direction of
magnetic field is also reversed.

3. State the direction of the magnetic field inside the bar

magnet.
Ans : [CBSE 2016]
In a magnet, magnetic field lines goes from S pole to
N pole.

4. Identify the poles of the magnet in the given figure.

7. Draw a diagram to represent a uniform magnetic field

in a given region.
Ans : [CBSE 2015]
Uniform magnetic field is represented by equidistant
parallel lines.

Ans : [CBSE 2016]

A1 is North Pole, B1 is South Pole because magnetic 8. What type of core is used to make an electromagnet?
field lines goes from north pole to south pole of the Ans : [CBSE 2015]
magnet. Soft iron core is used in making an electromagnet.

9. State the direction of magnetic field in the following

 case: 16. What will be the frequency of an alternating current
if its direction changes after every 0.01 s?
Ans : [CBSE 2011]
The direction of ac changes every 0.01 sec.
Thus time of one complete cycle = 0.02 sec
i.e. in 0.02 sec no. of cycle = 1
in 1 sec no. of cycle = 1 = 100 = 50
0.02 2
Ans : [CBSE 2014]
Frequency of ac = 50 Hz
Perpendicular to both current and force on the
conductor outward the plane of paper. 17. What is short-circuiting in an electric supply?
Ans : [CBSE2005]
10. Mention the voltage and frequency of current that we
receive at our house. When a neutral wire and live wire come in contact
Ans : [CBSE 2014] with each other short circuit takes place.

In our house we get AC of voltage 220 V and frequency 18. What constitutes the field of a magnet?
50 Hz. Ans : [CBSE 2006]
11. Name the type of current: (a) used in household The magnetic field is created by the magnet or when
supply (b) given by a cell. a charge particle is moving with some velocity in both
Ans : [CBSE 2014] cases they produce a magnetic field around them. The
magnetic field is due to current or magnetic material.
a. We use alternating current in our houses which
changes to direction and magnitude with time. 19. What is the advantage of the third wire of earth
b. A cell supply direct current (DC) or unidirectional connection in domestic appliances?
current which flows only in one direction only. Ans : [CBSE 2006]
12. State the rule which you use to find the direction of In case of any electric fault in domestic appliances,
induced current or state Fleming’s right hand rule. current may comes in appliance body. The third wire
Ans : [CBSE 2015] called earth wire transfer this current to the earth and
user remains safe from any such electric shock.
Fleming’s right hand rule gives the direction of current
produced in a conductor. According to Fleming’s right 20. How can you show that the magnetic field produced
hand rule, if we stretch right hand thumb, forefinger by a given electric current in the wire decreases as the
and middle finger perpendicular to each other in distance from the wire decreases?
such a way that thumb points the direction of force Ans : [CBSE 2006]
on a conductor and forefinger points the direction
If we bring a magnetic compass from a distance to
of magnetic field then middle finger will point the
near a current carrying conductor its deflection goes
direction of current produced in the conductor.
on increasing and when magnetic compass is brought
13. How can it be shown that a magnetic field exists away from the current carrying wire its deflection goes
around a wire through which a direct current is on decreasing which shows that magnetic field near
passing. current carrying wire is maximum and decreasing on
Ans : [Delhi 2014] increasing the separation.

When we put a small magnetic compass near a current 21. When is the force experienced by a current carrying
carrying conductor it gets deflected, which shows that conductor placed in a magnetic field the maximum?
a magnetic field is produced near a current carrying Ans : [CBSE 2009]
conductor.
A current carrying conductor experience maximum
14. How is the strength of the magnetic field at a point force in a magnetic field when the direction of current
near a wire related to the strength of the electric is perpendicular to the magnetic field.
current flowing in the wire?
22. How is the induced current in a secondary coil related
Ans : [CBSE 2009] to current in a primary coil?
The magnetic field strength at a point near a wire is Ans : [CBSE 2009]
directly proportional to the current strength in the
Induced current in a secondary coil may be more or
conductor.
lesser than the current in primary coil depending upon
15. An alternating electric current has a frequency of 50 the number of turns in secondary.
Hz. How many times does it change its direction in
23. What is the pattern of field fines inside a solenoid?
one second?
What do they indicate?
Ans : [CBSE 2011]
Ans : [CBSE 2010]
50 Hz ac changes its direction 100 times in 1 sec.
The magnetic field inside a solenoid is uniform in the
 form of parallel lines. A coil of many circular turns of insulated wire wrapped
closely in the form of a cylinder is called a solenoid.
24. How is the magnetic field produced in a solenoid used? In a current carrying solenoid magnetic field is same
Ans : [CBSE 2010] at all points inside it, i.e. field is uniform inside the
Magnetic field produced in a solenoid can be used in solenoid. The magnetic field inside a coil vary.
making a soft iron piece electromagnet.
33. An alpha particle (+ve charged particle) enters a
25. What does the direction of thumb indicate in the magnetic field at right angle to it as shown in figure.
right-hand thumb rule? Explain with the help of a relevant rule, the direction
of force acting on the alpha particle.
Ans : [CBSE 2010]
Thumb points the direction of current in the conductor
holding a straight conductor in right hand.

26. Mention the angle between a current carrying

conductor and magnetic field for which the force
experienced by this current carrying conductor placed
in magnetic field is largest? Ans : [CBSE 2016]
Ans : [CBSE 2012] Force on a-particle will be in the upward direction as
If the angle between a current carrying conductor and per Fleming’s left hand rule.
magnetic field is 90° then the force experienced by the
conductor is maximum. 34. An alternating electric current has a frequency of 50
Hz. How many times does it change its direction in
27. Suggest one way of discriminating a wire carrying one second? Give reason for your answer.
current from a wire carrying no current. Ans : [CBSE 2016]
Ans : [CBSE 2012] 100 times in one second because one complete cycle
When a magnetic compass is brought near a current involves two times change of direction.
carrying conductor it will be deflected. If magnetic
compass remains undeflected near a conductor then
there is no current in it.

28. What does the thumb indicated in Fleming’s right

hand rule?
Ans : [CBSE 2012]
Thumb indicate the direction of force on conductor
i.e. motion of the conductor.

29. Why are magnetic field lines closed curves?

Ans : [CBSE 2012]
By convention the magnetic field lines are the path
traced by north pole which emerges from north pole
and goes to the south pole and inside the magnet the
35. (a) Name the type of electric current generated by
direction of field lines are from south pole to north
the most of the power stations in our country.
pole, forming continuous closed path.
(b) Why is it preferred over the other type?
30. Write any one method to induce current in a coil. (c) State the frequency of the power supply generated
in India.
Ans : [CBSE 2013]
Ans : [CBSE 2016]
By moving a magnet towards the coil or vice versa,
current can be induced in the coil. (a) Alternating current
(b) AC can be transmitted at high voltage using step
up transformer to prevent loss in transmission.
TWO MARKS QUESTIONS (c) 50 Hz

36. (a) A compass needle gets deflected when brought

31. State two ways by which the strength of an near a current carrying conductor. Why?
electromagnet can be increased. (b) What happened to the reflection of needle when
Ans : [CBSE 2016] current in the conductor is increased?
By increasing the strength of current and number of Ans : [CBSE 2014]
turns of the solenoid we can increase the strength of (a) Near a current carrying conductor a magnetic
an electromagnet. field is produced which deflect the compass.
(b) With the increase in strength of current in the
32. Define a solenoid. How is it different from a coil? conductor strength of magnetic field also increases
Ans : [CBSE 2016] so there will be more deflection in compass.
37. Draw the patterns of magnetic field fines due to a bar b. Magnetic field lines in a solenoid.
magnet. The magnetic field fines are closed curves.
Why? 40. A compass needle is placed near a current carrying
wire. State your observation for the following cases
Ans : [CBSE 2014]
and give reason for the same in each case:
Magnetic field lines emerge out from the N-pole of a a. Magnitude of electric current in the wire is
bar magnet go to the S-pole and inside the magnet increased.
field lines goes from S-pole to N-pole thus form the b. The compass needle is displaced away from the
closed curves. wire.
Ans : [CBSE 2014]
a. Compass needle is deflected more because more
the current, more the magnetic field near the wire.
b. Magnetic field strength is inversely proportional
to the distance from current carrying wire. So
deflection will decrease in the compass needle
when brought away from wire.

41. What are magnetic field lines? How is the direction

of magnetic field at a point determined? Mention few
important properties of magnetic field lines.
Ans : [CBSE 2016]
38. (a) In a pattern of magnetic field fines due to a bar Magnetic field lines are the path traced by north pole
magnet, how can the regions of relative strength in a magnetic field. A tangent drawn to the magnetic
be identified? field lines gives the direction of magnetic field at that
(b) Compare the strength of field near the poles and point.
middle of a bar magnet. a. Magnetic field lines emerge out from the N-pole
Ans : [CBSE 2014] and go to the south pole and from S-pole to N-pole
(a) More the density of the magnetic field lines i.e. inside the magnet forming the closed curve.
more closer the magnetic field lines more the b. They do not intersect each other.
strength of magnetic field. 42. What is the nature of magnetic field produced by a
(b) Near the poles magnetic field lines are closer than straight current carrying circular coil? Explain with
the middle of a bar magnet. So magnetic strength the help of an experiment.
is more near poles than middle part of bar magnet.
Ans : [Delhi 2015]
39. Identify the type of magnetic fields represented by the Bend a wire in the shape of a circular loop. Pass the
magnetic field fines given below and name the type coil through a cardboard. Connect the free ends of
conductors which can produce them. the coil to a battery and a key. Sprinkle some iron
filings on the cardboard. Put on the key you will find
that the iron filings arrange themselves in the form of
concentric circles. The magnetic lines of forces near
each segment of wire are circular and form concentric
circles, whereas the lines of force near the centre of the
coil are almost straight lines.
The right hand thumb rule predicts the direction
of this magnetic field it states “Grasp the conductor
in the right hand with the thumb pointing in the
direction of current, and then the direction in which
the fingers curl gives the direction of the magnetic
Ans : [CBSE 2014] field.”

43. On what factors does the force experienced by a

current carrying conductor placed in a uniform
magnetic field depend?
Ans : [CBSE 2015]
The force experienced by a current carrying conductor
in a magnetic field depends upon—
a. length of the conductor
b. current in the conductor
c. magnetic field in which it is kept

a. Magnetic field lines of a current carrying circular 44. What is meant by the term “magnetic field lines”?
loop.
 List two properties of magnetic field lines. whether we require it or not.
Ans : [CBSE 2006] d. In series combination total potential difference
is divided among all appliances in proportion
Magnetic field lines are the path traced by a
to their resistance. So all appliance will not get
hypothetical north pole in the magnetic field of
required voltage to operate efficiently.
another magnet or current carrying conductor if it is
allowed to do so. 47. Explain what is short-circuiting and overloading in an
Properties: electric supply.
a. No two field lines are found to cross each other. Ans : [CBSE 2001]
b. Outside the magnet magnetic field lines travel
from N-pole to S-pole and inside the magnet from When live wire and neutral wire come in contact with
S-pole to N-pole. each other short circuit takes place. This may be due
to fault in electric circuit or when insulation of wire is
45. With the help of a neat diagram, describe how you damaged. During the short circuiting current increases
can generate induced current in a circuit. abruptly due to decrease in resistance in the circuit.
Ans : [CBSE 2006] This short circuiting leads the spark and house may
catch fire.
Take a coil of large number of turns and connect the
two ends of the coil with a galvanometer. Galvanometer Over loading means to draw the current by all
is a device used to detect the presence of current. electric appliances in the circuit more than maximum
permitted value of the current, overloading also leads
Now bring N pole of a strong magnet towards
the heating of wires which may damage the insulation
the coil. There is a momentary deflection in the
of wires.
galvanometer. Now bring the N pole away from
the coil, again there is a deflection in the opposite
direction in the galvanometer deflection in the
galvanometer shows that a current is induced in the
coil. The induced current can be produced by keeping
magnet stationary and giving movement to the coil,
or when both have a relative motion w.r.t. each other.

48. State the characteristics of magnetic force.

Ans : [CBSE 2002]
If a charge is moving in a magnetic field then
it experiences a force known as magnetic force
F = qVB sin q , B is magnetic force, q is angle between
B and V. This magnetic force
a. acts only when charge is moving
b. does not act when charge is at rest
c. is maximum when charge is moving perpendicular
to the magnetic field
d. does not act when charge is moving in the same
direction of magnetic field.

49. The flow of a current in a circular loop of a wire creates

46. Why is series arrangement not used for domestic a magnetic field at its centre. How can existence of
circuits? this field be detected? State the rule which helps to
Ans : [CBSE 2001] predict the direction of this magnetic field.
Ans : [CBSE 2004]
In domestic circuits, all appliances are connected in
parallel not in series because Take a cardboard and fix it. Now pass a thick copper
a. In series combination same current is passed wire having two holes giving the wire a circular shape.
through each appliances whereas they may need Connect the two ends of the wire with a cell and plug
different current. key. Sprinkle iron filings uniformly on the cardboard.
b. If one appliance fails to work then circuit will be Now plug in key and tap the cardboard gently a
broken and all other appliances will stop to work. number of times. The iron filings arrange themselves in
c. If one appliance is switched off others also will the pattern of concentric circles. Near each segment of
stop working i.e. all appliance will work together wire whereas near the centre of the coil these arrange
 almost in straight lines. Right hand thumb rule gives Ans : [CBSE 2004]
the direction of magnetic field i.e. if we hold a current The pattern of magnetic lines of force is in the form
carrying conductor in our right hand in such way that of concentric circles around the current carrying wire.
thumb points the direction of current, then the curls
of the fingers encircling the conductor will give the
direction of magnetic field around the conductor.

a. with the increase in current, magnetic field around

the conductor also

50. How does the strength of the magnetic field at the

centre of a circular coil of wire depend on: (i) the
radius of the coil (ii) the number of turns of wire in
the coil (iii) the strength of the current flowing in the
coil?
b. near the current carrying conductor magnetic field
Ans : [CBSE 2004] is more which decreases with increase in distance
The magnetic field at the centre of a current carrying from the wire.
circular coil is
a. inversely proportional to the radius ‘a’ of the coil
B \ a1
b. directly proportional to the number of turns in
the coil
c. directly proportional to the current I in the coil
B\I.

52. Draw the pattern of lines of force due to a magnetic

field through and around a current carrying loop of
wire. How would the strength of the magnetic field
51. Draw the pattern of lines of force due to a magnetic produced at the centre of the circular loop be affected
field associated with a current carrying conductor. if
State how the magnetic field produced changes a. the strength of the current passing through this
a. with an increase in current in the conductor and loop is double?
b. the distance from the conductor. b. the radius of the loop is reduced to half of the
 original radius? (1)
Ans : [CBSE 2004]
The pattern of lines of force due to a magnetic field
through and around a current carrying loop of wire is
shown below (2)
Ans : [CBSE 2010]
The figure is as shown below :

a. Strength of magnetic field is doubled when the

current through the loop is doubled B \ I .
b. Strength of magnetic field is doubled when the 56. What are permanent magnet and electromagnet?
radius of the loop is halved B \ r1 . Give two uses of each.
Ans : [CBSE 2010]
53. Draw the pattern of field lines due to a solenoid
Permanent Magnet: It has constant magnetic field
carrying electric current. Mark the north and south
around it. e.g. generator, loud speaker.
poles in the diagram.
Electromagnet: When a soft iron is placed in a solenoid
Ans : [CBSE 2004] it gets magnetised till there is current in solenoid, e.g.
The pattern of the magnetic field lines is as shown in electric bells, cranes.
figure.
57. Explain briefly different methods of producing induced
emf.
Ans : [CBSE 2010]
a. By mutual induction: If we change current in one
coil, a current is induced in the neighbouring coil.
b. By giving a relative motion to a magnet and coil
in its neighbourhood.

58. What is the role of fuse, used in series with any

electrical appliance? Why should a fuse with defined
rating not be replaced by one with a larger rating?
54. Differentiate overloading and short- circuiting.
Ans : [CBSE 2010]
Ans : [CBSE 2010] Fuse wire is safety device to prevent electrical devices
due to short circuiting or overloading. The fuse wire
Overloading means to draw current more than the
is rated for a maximum current which has high
permitted maximum current in the circuit which may
resistance and low melting point. When there is short
be due to connecting many appliances in one socket.
circuiting large current is passed in the circuit. Due
In short circuiting, when live wire and neutral to large current in fuse wire heat is produced and
wire come in contact with each other then resistance by melting fuse wire breaks the circuit to keep other
of the circuit becomes minimum consequently the appliances safe.
current in the circuit increases abruptly. It may be
If a fuse wire is replaced by an ordinary copper
due to damage of insulation of wire.
wire which has low resistance and high melting point
55. Identify the poles of the magnet in the given figure it will not melt and domestic appliance may get
(1) and (2). damaged due to excessive heat due to short circuiting
or overloading.

59. A magnetic compass shows a deflection when placed

near a current carrying wire. How will the deflection
of the compass get affected if the current in the wire is
increased? Support your answer with a reason.
Ans : [CBSE 2010]
If current is increased magnetic field around this
 conductor increases, the deflection in the galvanometer Which of the two observations is correct and why?
also increases. Ans : [CBSE 2011]
60. No two magnetic field lines can intersect each other. First observation is correct because when current
Explain. increases force also increase. From equation of force on
Ans : [CBSE2010] a current carrying conductor F = BIl. F \ I i.e. more
current more force on a current carrying conductor in
If two magnetic field lines intersect each other then a magnetic field.
at the point of intersection there will be two different
tangents pointing two different directions of magnetic 65. An electron enters a uniform magnetic field at right
field at a point which is not possible. angles to it as shown in the figure below. In which
direction will this electron move? State the rule
61. What is meant by the term magnetic field lines? List applied by you in finding the direction of motion of
any two properties of magnetic field lines. the electron.
Ans : [CBSE 2010]
The imaginary path traced by N-pole of a magnet in a
magnetic field is called magnetic field lines.
Properties:
a. Two magnetic field lines never intersect each
other.
b. Magnetic field lines are crowded near the poles
and near the mid part of magnets the density of
magnetic lines of force decreases.

62. Why does a current carrying Conductor experiences Ans : [CBSE 2011]
a force when it is placed in a magnetic field? State
As per Fleming’s left hand rule the electron
Fleming’s left hand rule.
will experience a force upward. So it will move
Ans : [CBSE 2011] perpendicularly outward.
When a current carrying conductor is placed in
a magnetic field it experiences a force due to
interaction between the two magnetic fields due to
current carrying , conductor and given magnetic field
of a magnet. If we hold our thumb, forefinger, and
middle finger perpendicular to each other in such a
way that forefinger points the direction of magnetic
field, middle finger points the direction of charge q
(direction of current in conductor), then thumb will
point the direction force acting upon the conductor.
Fleming’s left hand rule -stretch the forefinger,
63. A student performs an experiment to study the
the middle finger and the thumb of the left hand
magnetic effect of current around a current carrying
mutually perpendicular to each other in such a way
straight conductor with the help of a magnetic
that forefinger points the direction of magnetic field,
compass. He reports that:
middle finger points the direction of current (opposite
a. the degree of deflection of the magnetic compass
to the flow of electrons) then the thumb will point the
increases when the compass is moved away from
direction of force on the conductor (charge).
the conductor.
b. the degree of deflection of the magnetic compass 66. (a) What is the direction of magnetic field lines inside
increases when the current through the conductor a bar magnet and outside of it?
is increased. (b) What does the degree of closeness of the field lines
Which of the above observations of the student represent?
appears to be wrong and why?
Ans : [CBSE 2011]
Ans : [CBSE 2011]
The direction of magnet lines of force inside a bar
The first statement is wrong because the strength of magnet is from S-pole to N-pole. Outside the bar
magnetic field decreases when we move away from magnet these emerge out from N-pole and go to the
a current carrying conductor. So deflection in the
compass, instead of increasing must decrease. 67. A magnetic compass shows a deflection when placed
near a current carrying wire. How will the deflection
64. A student while studying the force experienced by a of the compass get affected, if the current in the wire
current carrying conductor in a magnetic field records is increased? Support your answer with a reason.
the following observations:
Ans : [CBSE 2011]
a. The force experienced by the conductor increases
as the current is increased. If the strength of current is increased then deflection
b. The force experienced by the conductor decreases of compass also increase because magnetic field is
as the strength of the magnetic field is increased. directly proportional to the current in the conductor.
 More magnetic field more deflection in the compass. a. \ r1 , i.e. magnetic field decreases with increase in
radius.
68. Draw magnetic field lines produced around a b. \ n , i.e. magnetic field increases with increase in
current carrying straight conductor passing through number of turns.
cardboard. How will the strength of the magnetic field
change, when the point where magnetic field is to be 71. Name and state the rule to determine the direction
determined, is moved away from the straight wire of a force experienced by a current carrying straight
carrying constant current? Justify your answer. conductor placed in a magnetic field which is
Ans : [CBSE 2012] perpendicular to it. Name a device that uses current
carrying conductor and magnetic field.
The strength of the magnetic field decreases when
the point where magnetic field is to be determined is Ans : [CBSE 2012]
moved away from the wire. Fleming’s left hand rule gives the direction of force
experienced by a current carrying straight conductor
placed in a magnetic field which is perpendicular to
it. According to Fleming’s left hand rule if we stretch
our left hand thumb, forefinger and middle finger
in such a way that forefinger points the direction of
magnetic field, middle finger points the direction of
current then thumb will give the direction of force on
the conductor.

69. Magnetic field lines are shown in the given diagram.

A student makes a statement that magnetic field
at X is stronger than at Y. Justify this statement.
Also, redraw the diagram and mark the direction of
magnetic field lines.

Ans : [CBSE 2012]

More the density of electric field lines more the
strength of magnetic field.

THREE MARKS QUESTIONS

72. (a) State Fleming’s left hand rule.

(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an
electric motor.
(i) Armature, (ii) Brushes, (iii) Split ring
Ans : [CBSE 2017]
70. How does the strength of the magnetic field at the (a) Fleming’s left hand rule: If we stretch thumb,
centre of a circular coil of a wire depend on: forefinger and middle finger of left hand
a. radius of the coil perpendicular to each other in such a way that
b. number of turns in the coil. forefinger points in the direction of magnetic field,
Ans : [CBSE 2012] middle finger points in the direction of current
then the thumb will point in the direction of
Magnetic field strength at the centre of a circular coil
motion/force on the current carrying conductor.
of a wire carrying current
(b) Principle of working of electric motor: A current
 carrying coil placed in a magnetic field experience 75. Define magnetic field. Describe an activity to draw
a torque. If the coil is free to move it will rotate in magnetic field lines around a bar magnet from one
the magnetic field. pole to another pole.
(c) (i) Armature: The soft iron core on which the coil Ans : [CBSE 2016]
is wound along with coils is called armature which
Magnetic field is the space around a magnet or a
enhances the power of motor.
current carrying conductor in which its magnetic force
(ii) Brushes: Brushes help in transfer of current
can be experience.
between coil and external circuit.
(iii) Split rings reverses the direction of current Fix a plane white drawing sheet on a drawing
after every half rotation of the coil so that the board. Now take a bar magnet and a compass. Place
direction of torque/force on the coil remains the magnet at the middle of the paper and mark its
and it continuous to rotate. boundary with the help of a pencil. Now place the
compass near its N pole of the magnet and marks
73. For the circular coil carrying current shown alongside, the positions of needle of the compass. Now move the
draw magnetic field lines. Decide which of its face compass on the drawing board. Coinciding south pole
behaves as North Pole and which face as South Pole. of the compass with the previous marked point of N
Give reason to justify your answer. pole of the needle and so on, move forward from one
end
(N pole) to the another end (S pole) of the bar magnet.
Join all the marked points. You will get magnetic lines
of force.

Ans : [CBSE 2014, 2016]

From the front face magnetic field emerges out of the
coil and enters out from the back face so front face
will behave as north pole and back face as south pole.

76. Find the minimum rating of fuse that can be safely

used on a line on which two 1.1 kW, electric geysers
are to run simultaneously. The supply voltage is 220
V.
Ans : [CBSE 2015]

I = Total Power = nP
V V

= 2 # 1.1 kW
220 V

= 2 # 1.1 # 1000 W = 10 A
220 V
74. A uniform magnetic field is directed vertically So a fuse wire of rating must be greater than 10 A.
upwards. In which direction in this field should an
a-particle (which are positively charged particles) be 77. Can a freely suspended current carrying solenoid
projected so that it is deflected south ward? Name stay in any direction? Justify your answer. What will
and state the rule you have used to find the direction happen when the direction of current in the solenoid
in this case. is reversed? Explain.
Ans : [CBSE 2016] Ans : [CBSE 2015]
Forefinger - direction of magnetic field (upwards). No, current carrying solenoid behaves like a bar
Thumb - direction of force (southwards) Middle finger magnet and will stay only geographical N and S
gives direction of current or direction of positively direction. If the direction of current is reversed then
charged particle (East) i.e. from west to east a particles the polarity of the magnet will change and hence will
must be projected. rotate through an angle of 180°.
78. What is meant by electromagnetic induction? State carrying circular coil changes, if we increase the:
the rule which helps in determining direction of a. value of current flowing through it?
induced current. b. distance of point P from the coil?
Ans : [CBSE 2015] c. number of turns of the coil?
Electromagnetic induction is the phenomenon of Ans : [CBSE 2011, 2014]
production of emf (potential difference) or current a. Magnetic field is directly proportional to current
in a coil due to change in magnetic field around it. so magnetic field increases when current increases.
Fleming right hand rule: If we stretch our right hand b. If we increase the distance of point P, magnetic
thumb, forefinger and middle finger perpendicular to field decreases.
each other in such a way that forefinger points the
direction of magnetic field, and thumb points the
direction of force acting on the conductor (motion
of the conductor), then the middle finger points the
direction of induced current in the conductor.

79. Horizontal component of earth’s magnetic field at a

place is uniform and its direction is south to north. A
high current through a horizontal power line flows at
this place from west to east. Consider two points A
and B at equal distances from the wire, respectively
above and below it. Giving reason explain where is the
field more at A or at B. c. On increasing the number of turns magnetic field
Ans : [CBSE 2014] increasing.

The direction of magnetic field due to current at A 82. What happens to the deflection of the compass needle
is from north to south and at B from south to north. placed at a point near current carrying straight
Therefore, at A earth’s magnetic field and field due to conductor:
current are in opposite direction and at B earth’s a. if the current is increased?
magnetic field and magnetic field due to current are b. if the direction of current in the conductor is
in same direction. changed (reversed)?
c. if compass is moved away from the conductor?
Ans : [CBSE 2011, 2014]
a. If the current increases deflection of compass
increases.
b. If the direction of current is reversed the deflection
in the compass needle is also reversed.
c. Deflection of the compass needle decreases when
compass is moved away from the conductor.

83. Name any three factors on which the magnitude of the

magnetic field due to solenoid depends.
Ans : [CBSE 2014]
Factors on which the magnitude of the magnetic field
80. A coil of insulated wire is connected to a galvanometer.
due to solenoids
Explain what happens if a bar magnet with its north
a. number of turns in the solenoid
pole towards one face of the coil is:
b. area of cross section of the coil
a. moved quickly towards the coil,
c. strength of current in solenoid
b. kept stationary inside the coil, and
c. moved quick away from the coil? 84. State the condition for electromagnetic induction to
Ans : [CBSE 2014] take place. A cylindrical bar magnet is kept along the
When a bar magnet is moved towards the coil there is axis of a circular coil as shown in the figure. Will
change in magnetic field in there be a current induced in the coil if the magnet is
a. coil so a current is induced in the coil so rotated about its axis? Discuss.
galvanometer gives a deflection.
b. when magnet is kept stationary in the coil then
due to no change in the magnetic field no current
is induced in the coil.
c. when magnet is moved quickly away from the coil
again there is change in magnetic field associated
with the coil so again a current is induced but in
the opposite direction.
Ans : [CBSE 2014]
81. How will the magnetic field produced in a current
Electromagnetic induction
 a. Either coil or magnet or both must have a relative 87. (a) Electric fuse is an important component of all
motion between them. domestic circuits. Why?
b. If there is a change in current in a coil then current (b) An electric oven of rating 2 kW, 220 V is operated
will be induced in the another neighbouring coil. in a domestic circuit with a current rating of 5 A.
No current is induced because there is no change What result would you expect? Explain.
in magnetic field. Ans : [CBSE 2010]
Electric fuse is a safety device which has high resistance
85. Draw a diagram to show how a magnetic needle
and low melting point and prevents electric appliances
deflects when it is placed above or below a straight
during short circuiting and overloading. By melting
conductor carrying current depending on the direction
itself, a fuse break the circuit.
of the current in the conductor.
Ans : [CBSE 2010] 88. Name two safety measures commonly used in electric
circuits and appliances, what precautions should be
taken to avoid the over loading of domestic electric
circuits?
Ans : [CBSE 2010]
Proper earthing and using a fuse load in the electric
circuit must be as per rating of the fuse and do not
connect to many plugs in a single socket.

89. Why does a current carrying conductor kept in a

magnetic field experience force? On what factors does
the direction of this force depend? Name and state the
86. (a) Describe an activity to draw a magnetic field line rule used for determination of direction of this force.
outside a bar magnet from one pole to another. Ans : [CBSE 2010]
(b) List any two properties of magnetic field lines.
Around a current carrying conductor a magnetic field
Ans : [CBSE 2010] is produced. When it is placed in a magnetic field then
(a) Fix a plane white drawing sheet on a drawing both fields interact each other, and current carrying
board. Now take a bar magnet and a compass. conductor experience a force.
Place the magnet at the middle of the paper and Fleming’s left hand rule: If we stretch right hand
mark its boundary with the help of pencil. Now thumb, forefinger and middle finger perpendicular
place compass near N-pole of bar magnet and the to each other in such a way that forefinger points
position of needle of the compass. Now move the the direction of magnetic field, middle finger points
compass on the drawing board coinciding S-pole the direction of current, then thumb will point the
of the compass with the previous marked point of direction of force on the conductor.
N of the needle and so on move forward from one
end (N-pole) to the S-pole of the bar magnet. Join 90. What does the direction of thumb indicate in the right
all the marked points. You will get magnetic lines hand thumb rule? In what way this rule is different
of force. from Fleming’s left hand rule?
Ans : [CBSE 2010]
Thumb indicate the direction of current in a straight
conductor held in right hand. Fleming’s left hand
rule gives the direction of force on a current carrying
conductor placed in magnetic field.
Fleming’s left hand rule : If we stretch right hand
thumb, forefinger and middle finger perpendicular
to each other in such a way that forefinger points
the direction of magnetic field, middle finger points
the direction of current, then thumb will point the
direction of force on the conductor.

91. Under what condition does a current carrying

conductor kept in a magnetic field experience
maximum force? On what other factors does the
magnitude of this force depend? Name and state the
rule used for determination of direction of this force.
(b) Properties of magnetic field lines. Ans : [CBSE 2011]
(i) Magnetic field lines do not intersect each
other. Force on a current carrying conductor in a magnetic
(ii) Magnetic field lines emerge out at N-pole and field depends upon
goes to the S-pole whereas in magnet these a. length of the conductor
travel from S-pole to N-pole. b. strength of the magnetic field
c. strength of the current
 d. angle between direction of magnetic field and b. AG generators are used to produce AC.
current. c. AC voltage can be increased or decrease with the
Fleming’s Left Hand Rule: help of a transformers.
Fleming’s left hand rule gives the direction of force
95. State one main difference between ac and dc. Why
experienced by a current carrying straight conductor ac is preferred over dc for long range transmission of
placed in a magnetic field which is perpendicular to electric power? Name one source each of dc and ac.
it. According to Fleming’s left hand rule if we stretch
our left hand thumb, forefinger and middle finger Ans : [CBSE 2012]
in such a way that forefinger points the direction of The magnitude and direction of ac remains same
magnetic field, middle finger points the direction of whereas a.c. changes its magnitude and direction
current then thumb will give the direction of force on periodically. Low AC voltage can be increase to high
the conductor. voltage to prevent loss in electric energy during its
long distance transmission.
AC generator and DC generator/or cell.

96. (a) Mention the colour code used for live, neutral and
earth wire.
(b) You want to connect a 2 kW electric oven in the
electric circuit. In which power line would you
connect it and why? What may happen if you
connect it wrongly in the other power line?
Ans : [CBSE 2013]
(a) Live wire – Red
92. A coil made of insulated copper wire is connected to
a galvanometer. What will happen to the deflection Neutral wire – Black
of the galvanometer if this coil is moved towards a Earth wire – Green
stationary bar magnet and then moved away from it? (b) 2 kW electric iron draws large current. If it is
Give reason for your answer and name the phenomenon connected to a socket of 5Athen fuse will be
involved. blown. So it is connected in power socket of 15 A.
Ans : [CBSE 2011]
In both the case there is a change in magnetic field FIVE MARKS QUESTIONS
associated with the coil, an induced current is produced
in the coil, but in opposite direction. This phenomenon
is called electromagnetic induction (EMI). 97. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
93. What is meant by overloading of an electrical circuit?
(c) Explain the function of the following parts of an
Explain two possible causes due to which overloading electric motor.
may occur in household circuit. Explain one precaution
that should be taken to avoid the overloading of (i) Armature (ii) Brushes (iii) Split ring
domestic electric circuit. Ans : [CBSE 2017]
Ans : [CBSE 2012] (a) Fleming’s left hand rule state that if the thumb,
Connecting large number of electric appliances in forefinger and middle finger are stretched
one socket whose load is more than the maximum perpendicular to each other in such a way that
permitted limit. The two possible cause are forefinger indicates the direction of magnetic field,
a. all of a sudden supply of high voltage and middle finger indicate the direction of current
b. too many devices connected in a single socket. in the conductor then thumb will indicate the
direction of force on the conductor.
Precautions:
(b) The principle of electric motor is that when a
a. use of voltage regulator,
current carrying coil is placed in a magnetic field
b. load of a socket must be greater than its permitted
it experiences a torque and if the coil is allowed it
rating.
rotates in the magnetic field.
94. Write one difference between direct current and (c) Function of the parts of an electric motor :
alternating current. Which one of the two is mostly (1) Armature: Armature is a large number
produced at power stations in our country? Name one of turns of the coil on soft iron core which
device which provides alternating current. State one rotates in magnetic field.
important advantage of using alternating current. (2) Brushes: They allow current to pass from
external source to armature.
Ans : [CBSE 2012]
(3) Split rings: Split rings are of copper, splits into
Direct current has constant magnitude and two halves and make a connection between
unidirectional current. Alternating current changes its armature and brushes.
magnitude and direction alternatively.
a. Alternating current is produced in power stations 98. (a) Explain what is the difference between direct
in India. current and alternating current? Write one
 important advantage of using alternating current. (ii) In bar magnet, magnetism is permanent but
(b) An air conditioner of 2 kW is used in an electric in solenoid it exists only till there is a current
circuit having a fuse of 10 A rating. If the potential in solenoid.
difference of the supply is 220 V, will the fuse
be able to withstand, when the air conditioner is
switched on? Justify your answer.
Ans : [CBSE 2016]
(a) Direct current is a unidirectional current with
constant magnitude. Alternating current is a
current which change its magnitude and direction
after a fixed period. AC voltage can be increased
or decreased. Where is dc voltage cannot be
increased or decreased. AC can be transmitted to
long distances with lesser power loss.
(b) Given P = 2 kW and V = 200 volt,
Power, P = VI & I = VP
I = 2000
220 = 9.09 A
The rating of the fuse wire is 10 A which is greater
than current drawn by air conditioner so when air
conditioner is switched on, fuse will not blow off.

99. (a) Describe an activity to show the pattern of

magnetic field fines of a bar magnet, with the help
of a cardboard piece and iron filings.
(b) Compare the field of a bar magnet with that of a
solenoid with the help of figure.
Ans : [CBSE 2016]
100. (a) Describe an activity to determine the direction
(a) Fix a white paper sheet on a drawing board with of magnetic field produced by a current carrying
the help of copper pins. Keep a bar magnet in the straight conductor. Also show that the direction
centre of the paper and sprinkle some iron filings of the magnetic field is reversed on reversing the
uniformly around the bar magnet. Tap the board direction of current.
gently. Iron filings arrange themselves in a pattern (b) An a -particle, (which is a positively charged
as shown in figure. These iron filings near the bar particle) benters, a uniform magnetic field at
magnet align themselves along the magnetic field right angles to it as shown below. Stating the
lines. relevant principle explain in which direction will
this a-particle moves?

Ans : [CBSE2016]
(a) Fix a cardboard and pass a straight wire through a
hole in cardboard and connect the two ends of the
(b) A current carrying solenoid behaves as a bar
wire with a cell through a rheostat and key with
magnet one end of the solenoid behaves like a N
a cell. Sprinkle iron filings uniformly on the card
pole and another end as S pole like two poles in
board. Pass the current in the wire and gently tap
bar magnet, so the field lines of a solenoid and bar
the card board. You would find that iron filings
magnet appear same in many ways:
align themselves in concentric circles around the
(i) Magnetic lines of force inside the body is
copper wire which represents the magnetic field
strong and uniform.
around the current carrying conductor. The
(ii) In both the cases stronger field exists at the
direction of magnetic field changes on reversing
poles compared to the middle part.
the direction of current.
Dissimilarities
(b) According to Fleming’s left hand rule the force on
(i) In bar magnet, the poles are not exactly at
the oc-particle will be inwards perpendicular to
the ends of the magnet, in solenoid poles can
the plane of paper, so \-particle will move in the
be considered to be lying at the edges.
direction of force.
 In both the cases of a current carrying solenoid and
bar magnet the magnetic lines of forces inside the
body is strong and uniform. In both the cases there
exists stronger magnetic field at the poles compared
to the middle parts.
Dissimilarities:
(i) The poles in a bar magnet do not exist at the
extreme ends of the magnet whereas in solenoid
the poles can be considered to be lying at the
edge.

101. Explain the meanings of the words “electromagnetic”

and “induction” in the term electromagnetic induction.
List three factors on which the value of induced current
produced in a circuit depends. Name and state the rule
used to determine the direction of induced current.
State one practical application of this phenomenon in
everyday life.
Ans : [CBSE 2014]
The word electromagnetic means that an electric
potential dipole is being produced in a coil due to (ii) In a bar magnet, magnetism is retained naturally,
change in magnetic field. The word induction means but in solenoid magnetism is there so long current
that the current has been induced. The value of flows through it.
induced current produced in a circuit depends on the
following factors: 103. (a) State the function of ‘a fuse’ in an electric circuit.
a. number of turns in given coil How is it connected in the domestic circuit?
b. area of each turn in coil (b) An electric fuse of rating 3A is connected in a
c. rate of change of magnetic field. circuit in which an electric iron of power 1.5 kilo
The rule is Fleming’s right hand rule. Stretch watt is connected which operates at 220 V. What
the thumb, forefinger and middle finger of right- would happen? Explain.
hand perpendicular to each other that forefinger Ans : [CBSE 2015]
indicates the direction of magnetic field, thumb gives (a) Fuse is a safety device to prevent the damage of
the direction of motion (or force) of the conductor, electrical devices from short circuit or overloading.
then middle finger will point the direction of induced A fuse is connected in series with the circuit.
current. (b) Given Power P = 1.5 kW = 1500 Watt and
Application: AC generator or DC generator. V = 220 Volts.
102. What is a solenoid? Sketch magnetic field lines Power P = VI & I = VP = 1500
220 = 6.8 A
produced around a current carrying solenoid. Mark The rating of fuse is 3A which is lesser the current
the region where field is uniform. Compare its field drawn by electric iron 6.8 A. So fuse wire will be
with that of a bar magnet. blown.
Ans : [CBSE 2015] 104. (a) Draw magnetic field lines of a bar magnet. “Two
A solenoid is a large number of insulated turns of the magnetic field lines never intersect each other”.
copper wire in the shape of helix (or cylinder). Why?
The patterns of the magnetic field lines around a (b) An electric oven of 1.5 kW is operated in a
current carrying solenoid is as given in figure. At the domestic circuit (220 V) that has a current rating
centre of the solenoid the magnetic field is uniform of 5 A. What result do you expect in this case?
and magnetic field lines are parallel. Explain.
Similarities: Ans : [CBSE 2014]
 (a) Magnetic field lines around a bar magnet. 2- distance of the point from the wire \ I1
By decreasing current or increasing the distance
of the point from the wire, strength of magnetic
field also decreases.

107. (a) Name two electrical appliances of daily use in

which electric motor is used.
(b) Name and state the principle on which an electric
motor works.
Ans : [CBSE 2014]
(a) Drill machine, fan, grinder
(b) An electric motor works on the Fleming’s left
If the two magnetic field lines would intersect hand rule. When a current carrying coil is placed
with each other than at that point there will be in a magnetic field it experience a torque due to
two different directions of magnetic field which is which it rotates.
not possible. Fleming’s left hand rule-stretch left hand, thumb,
(b) Given Power P = 1.5 kW = 1500 Watt and forefinger and middle finger perpendicular to each
V = 220 Volts. other in such a way that forefinger indicates the
Current drawn I = ^P/V h = ^1500/220h A direction of magnetic field, middle finger indicates
the direction of current in the conductor then
I = 7 A (approx). thumb will point the direction of force on the
As the current drawn by the oven is 7 A which is conductor,
larger than the rating of the fuse (5A) so fuse will
blow off and circuit will be broken. 108. (a) What is an electromagnet? What does it consist
of?
105. (a) Explain any three properties of magnetic field (b) Name one material in each case which is used to
lines. make a : (i) permanent magnet (ii) temporary
(b) Give two uses of magnetic compass. magnet.
Ans : [CBSE 2014] (c) Describe an activity to show how you can make
(a) Properties of magnetic field lines: an electromagnet in your school laboratory.
1. Magnetic field lines emerge from N pole Ans : [CBSE 2006]
and merge at S pole outside a bar magnet a. A soft metal core made into a magnet by
and travel from S pole to N pole inside the the passage of electric current through a coil
magnet. surrounding it. It consists a soft iron core or its
2. These are continuous and closed curves. alloy and a solenoid conductor coil around the
3. Two field lines never intersect each other. core.
(b) Uses of magnetic compass : b. (i) To make a permanent magnet alloy Alnico
1. In navigation it is used to find direction. is used. (ii) Soft iron is used to make temporary
2. It is used to detect the magnetic field. magnet.
3. It can be used to test whether a substance is c. Take a long nail and put it into a solenoid of
magnetic or not. insulated copper wire. Pass the strong current in
106. (a) An electric current is passed in a horizontal copper
the solenoid the nail inside the solenoid becomes
wire from east to west. Explain your observations magnetised. This is called electromagnet.
when a compass needle is placed (i) below this 109. (a) Draw a schematic labelled diagram of a domestic
wire, (ii) above the wire. Draw inference from wiring circuit which includes (i) a main fuse (ii) a
your observations. power meter (iii) one light point and (iv) a power
(b) List the factors on which the strength of the plug.
magnetic field due to a straight conductor carrying (b) Why is it necessary to connect an earth wire to
current depend. How should these be changed to electric appliances having metallic covers?
decrease magnetic field at a point?
Ans : [CBSE 2005]
Ans : [CBSE 2014]
a.
(a) The direction of deflection of a magnetic compass
needle depends upon the direction of the magnetic
field at that point. The direction of the magnetic
field due to a current carrying wire is given by the
right hand screw rule. The direction of magnetic
field below and above the wire is opposite so
deflection in compass needle changes as well i.e,
the deflection is reverse direction.
(b) The factors affecting strength of the magnetic field
due to a straight wire carrying current:
1. magnitude of current in the wire \ I b. The earth wire carry current due to any leakage
or defective electric appliance to the earth keeping
 human beings safe preventing from any electric instruments? Why is it necessary to earth the
shock. metallic electric appliances?
(b) Explain what is short-circuiting and overloading
in an electric supply.
(c) What is the usual capacity of the fuse wire in the
line to feed:
(i) lights and fans?
(ii) appliances of 2 kW or more power?
Ans : [CBSE 2007]
(a) We can get an electric shock on touching a faulty
appliance, caused by the leakage of current from
the appliance. Earthing provides a safety measure
c. Properties of magnetic field lines against the electric shock caused by the leakage of
(i) They emerge from the north pole and merge current. Earth wire brings this leakage current to
at south pole of a bar magnet. the ground by a earth wire and we remains safe.
(ii) They do not intersect with each other. (b) Short circuiting takes place when a live wire and
(iii) They emerge and merge normal to the surface neutral wire come in contact with each other due
of magnet to damage of insulation of these wires. Due to
short circuiting, resistance of the circuit becomes
110. (a) What is meant by a ‘magnetic field’ ? minimum and a very high current is passed
(b) How is the direction of magnetic field at a point through the circuit which produces spark and
determined? heat and may lead a fire in the house. Overloading
(c) Describe an activity to demonstrate the direction when the amount of current flowing through the
of the magnetic field generated around a current circuit exceeds the rating of the protective devices
carrying conductor. it is said that circuit is overloaded. It is a situation
(d) What is the direction of magnetic field at the in which many electrical appliances are connected
centre of a current carrying circular loop? in a single socket. It will draw more current, may
Ans : [CBSE 2007] lead the burst of fire in building.
a. Magnetic field is the space around a magnet or a (c) (i) Bulbs, fans etc. – 5A, (ii) Heater – Micro-oven,
current carrying conductor in which its magnetic Electric iron – 15A
force can be experienced.
112. Describe in short an activity to:
b. A magnetic compass is used to demonstrate the
a. demonstrate the pattern of magnetic field lines
direction of the magnetic field generated around a
around a straight current carrying conductor, and
current carrying conductor.
b. find the direction of magnetic field produced for
c. Fix a cardboard and insert a wire to pass through
a given direction of current in the conductor.
its centre normal to the plane of the card board.
Name and state the rule to find the direction of
Sprinkle iron filings on card board uniformly. Pass
magnetic field associated with a current carrying
the current in the wire. Tap the cardboard gently.
conductor. Apply this rule to determine the
You will find that iron filings align themselves
direction of the magnetic field inside and outside
in the concentric circles around the wire. These
a current carrying circular loop lying horizontally
circles represents magnetic field lines around the
on a table. Assume that the current through the
conductor.
loop is anticlockwise.
d.
Ans : [CBSE 2010]
(a) Fix a cardboard and pass through its centre a
thick copper wire AB connected with a cell of
12 V through a rheostat, an ammeter and plug
key as shown in figure. Sprinkle the iron filings
uniformly on the cardboard. Plug in the key, tap
the cardboard gently a number of times. Iron
filings align themselves in a pattern of concentric
circles around the copper wire, which represents
the magnetic field lines.

At the centre of circular loop, the magnetic field

lines are straight.

111. (a) What is the function of an earth wire in electrical

 (b)
(b) The direction of magnetic field so produced a. Name the type of current in two cases.
around a current carrying conductor can be find b. Identify any one source for each type of current.
with the help of a magnetic compass. When we c. What is the frequency of current in case (b) in
put a magnetic compass at any point of these field our country?
fines it get deflected. The direction of deflection d. On the basis of these graphs list two differences
of the compass needle is the direction of magnetic between the two currents.
field. e. Out of the two which one is used in transmitting
electric power over long distances and why?
Ans : [CBSE 2010]
a. (i) DC (ii) AC

If the direction of current is reversed the direction

of magnetic field is also reversed. The direction b. (i) cell, (b) AC generator
of magnetic field can be found by using Ampere’s c. 50 c/s or 50 Hz.
right hand thumb rule. According to it, if we d. (i) Magnitude of DC is constant magnitude of AC
hold a straight conductor in our right hand such is varying
that thumb points the direction of current in the (ii) DC is unidirectional ac changes its direction
conductor after a fixed period.
e. AC can be transmitted by changing it at high
113. In our daily life we use two types of electric current voltage with the help of transformer to minimise
whose current-time graphs are given below: loss in transmission.

114. (a) Describe an experiment with a diagram to

show that force is exerted on a current carrying
conductor when placed perpendicular in a
magnetic field.
(b) How will this force change if current in the
conductor is increased?
(c) Name a device that uses the above principle.
Ans : [CBSE 2010]
a. Take a small metal rod AB and suspend it from
a stand with the help of two connected wire. Put
(a) the rod in between the horse shoe magnet in such
a way that rod remains in between the two poles.
Pass the current in the rod through the two wires.
You would find that the rod is deflected towards
the left. Now reverse the direction of current the
rod is deflected in opposite direction. This shows
that a force is experienced by a current carrying
conductor in magnetic field.
b. If the current in the conductor is increased then
more force will act on the rod, and get more
 deflected. entering first?
c. Electric motor. (ii) withdrawn from inside the coil?
(iii) held stationary inside the coil?
(b) Name the above phenomenon and mention the
name of the scientist who discovered it. State the
law that relates the direction of current in the coil
with the direction of motion of the magnet.
Ans : [CBSE 2011]
a. (i) Galvanometer gives a deflection
(ii) Again galvanometer gives a deflection but in
opposite direction.
(iii) No current is induced in the coil so no
deflection in the galvanometer.
b. Electromagnetic induction (EMI):
Faraday discovered it. Fleming’s right hand rule
gives the direction of induced current in the coil.
If we stretch right hand thumb, forefinger and
middle finger perpendicular to each other in such
115. (a) Which effect of the electric current is utilised in
a way that thumb gives the direction of motion
the working of an electrical fuse?
of the conductor, forefinger gives the direction
(b) A fuse is connected in series or in parallel in
of magnetic field then middle finger will give the
household circuit?
direction of current induced in the conductor.
(c) Draw a schematic labelled diagram of a domestic
circuit which has a provision of a main fuse, meter, 118. (a) When do we state that an electrical appliance is
one light bulb and a switch socket. earthed? Mention the function of earth wire in
Ans : [CBSE 2010] electric lines. Why is it necessary to earth the
a. Heating effect of current electric appliances having metallic body?
b. In series in the household circuit (b) Explain what is short circuiting and overloading
c. in an electric supply.
Ans :
(a) When metal body of an electric appliance is
connected to a wire which is connected to a metal
plate buried deep inside the earth is said to be
electrically earthed.
(b) If due to damaged insulation, live wire and neutral
wire come in contact with each other then it is
said to be short circuiting overloading. A circuit
over load occurs when the amount of current
flowing through the circuit exceeds the rating
116. Answer the following questions: of the protective device. Every electric circuit
a. What is the direction of magnetic field lines in a wiring system must be protected against
outside a bar-magnet? overloading. It happens when too many electric
b. Why two magnetic field lines cannot intersect appliances are connected into a single socket.
each other?
c. What is indicated by crowding of magnetic field 119. (a) Define electromagnetic induction.
lines in a given region? (b) Two coils P and S are wound over the same iron
d. What is the frequency of ac in India? core. Coil P is connected to battery and key
e. State one advantage of ac over dc. the coil S is connected to galvanometer. Draw a
Ans : [CBSE 2011] suitable diagram of this arrangement and write
your observations when:
a. From N pole to S pole (i) current in the coil P is started by closing the
b. If two magnetic field lines would intersect each key.
other then at the point of intersection there would (ii) current continues to flow in coil P.
be two different directions of magnetic field which (iii) current in coil P is stopped by removing the
is not possible. key.
c. Magnetic field strength is more in that region.
d. 50 cycles per sec (c/s) or Hz. Explain the reason for such observations.
e. AC can be step up for transmission over a longer Ans : [CBSE 2012]
distances with less power loss. a. The phenomenon by producing a current in a coil
by changing magnetic field associated with it or
117. (a) A coil of insulated copper wire is connected to a
by changing a current in the neighbouring coil
galvanometer. What will happen if a bar magnet
is called electromagnetic induction. Current so
is:
produced is called induced current.
(i) pushed into the coil with its north pole
 b. (i) When key K is closed due to increasing current the circuit and justify your answer.
a magnetic field is produced which is changing.
In this changing magnetic field coils is kept so an
induced current flow through it, so galvanometer
shows a deflection.
(ii) After some time current reaches maximum
and becomes constant in P coil. There is
no change in current so there is no change
in magnetic field associated with coil S and (b) Give one difference between the wires used in the
hence no induced current in coil S. Deflection element of an electric heater and in a fuse.
in galvanometer becomes zero. (c) List two advantages of parallel connection over
series connection.
Ans : [CBSE 2012]
(a) Errors in the circuit
(i) Fuse wire is connected in neutral wire (N)
where as it must be connected in live wire
(L).
(ii) Circuit of bulb B2 is incomplete.
(b) Element of electric heater has high resistance and
high melting point whereas a fuse wire has high
(iii) Current becomes zero from maximum in coil resistance and low melting point.
P and hence galvanometer shows a deflection (c) Advantages of parallel connection over series
but now it is in opposite direction. connection.
(i) In parallel combination if one appliance fails
120. Two coils C1 and C2 are wrapped around a non- to work others keep working.
conducting cylinder. Coil C1 is connected to a battery (ii) Potential difference across each appliance
and key and C2 with galvanometer G. On pressing the remains same.
key (K), current starts flowing in the coil C1 State
122. (a) Write the values of the following physical quantities
your observation in the galvanometer.
in connection with domestic power supply in our
country: (i) potential difference between live wire
and neutral wire. (ii) frequency of ac.
(b) Explain the role of the following as safety measure
in domestic electric appliance/circuits: (i) earth
wire (ii) fuse.
Ans : [CBSE2012]
(a) (i) 220 V, (ii) 50 Hz
(b) Safety measure in electric appliance/circuits:
a. What key K is pressed on. (i) Earth wire is a safety device to protect us
b. When current in the coil C1 is switched off. from electric shock due to leakage of current
c. When the current is passed continuously through or faulty electric appliances. An earth wire
coil C1. is a thick copper wire connected to a metal
d. Name and state the phenomenon responsible for plate buried deep in the earth. The metallic
the above observation. Write the name of the rule body of the electric appliance is connected to
that is used to determine the direction of current the earth wire, it provides a low resistance
produced in the phenomena. conducting path and leaked current goes to
deep in the earth and human beings do not
Ans : [CBSE 2012,14]
get a fatal electric shock.
a. Induced current in coil C2 is produced so (ii) Fuse: It is also a safety device. It is a wire of
galvanometer shows a deflection. an alloy with low melting point. If a current
b. Again galvanometer shows a deflection but in greater than a particular values flows in the
opposite direction to the previous one. circuit it will melt and circuit is broken and
c. There will be no deflection in galvanometer. stops power supply in the circuit.
d. This phenomenon is called electromagnetic
induction. The phenomenon in which a changing 123. What is a solenoid? Draw the magnetic line of forces
magnetic field in a coil induces a current in another for solenoid and a bar magnet. Compare the two and
coil kept near it. Fleming’s right hand rule is used state one similarity.
to find the direction of induced current. Ans : [CBSE2013]

121. (a) The given figure shows a domestic electric circuit. A solenoid is a large number of turns of insulated
Study this circuit carefully. List any two errors in copper wires having shape of a cylinder or helix.
Magnetic field are given in following figures.
(a) Fix a white paper sheet on a drawing board with
the help of copper pins. Keep a bar magnet in the
centre of the paper and sprinkle some iron filings
uniformly around the bar magnet. Tap the board
gently. Iron filings arrange themselves in a pattern
as shown in figure. These iron filings near the bar
magnet align themselves along the magnetic field
lines.

(b) A current carrying solenoid behaves as a bar

magnet one end of the solenoid behaves like a N
pole and another end as S pole like two poles in
bar magnet, so the field lines of a solenoid and bar
magnet appear same in many ways:
(i) Magnetic lines of force inside the body is
strong and uniform.
(ii) In both the cases stronger field exists at the
poles compared to the middle part.
Dissimilarities
(i) In bar magnet, the poles are not exactly at
the ends of the magnet, in solenoid poles can
be considered to be lying at the edges.
(ii) In bar magnet, magnetism is permanent but
in solenoid it exists only till there is a current
in solenoid.
Chap 3 : Metals and Non-Metals www.cbse.online

CHAPTER 3
Metals and Non-Metals

ONE MARK QUESTIONS room temperature.

Ans : [CBSE 2013]
Mercury is a metal and Bromine is a non-metal present
1. Give one most suitable word for the following as a liquid at room temperature.
statements:
a. Metal oxides which show basic as well as acidic 10. Name two metals which react with dilute HNO3 to
behaviour. evolve H2 gas.
b. Iodine, a shining non-metal. Ans : [CBSE 2013]
Ans : [CBSE 2015] Mn and Mg.
a. Amphoteric oxides.
b. Lustrous. 11. What is formed when sodium absorb moisture from
air? Give equation also.
2. Write the chemical equation for the reaction taking Ans : [CBSE 2013]
place when steam is passed over hot Aluminium?
Sodium hydroxide and hydrogen gas is formed:
Ans : [CBSE 2015] 2Na(s) + 2H2O(l) $ 2NaOH(aq) + H2(g)
Heat
2Al(s) + 3H2O(aq) Al2O3(S) + 3H2(g)
12. Why sulphide and carbonate ores are converted into
3. What happens when carbon dioxide is compressed in oxides?
water at high pressure? Ans : [CBSE 2013]
Ans : [CBSE 2015] It is because oxides are more easier to be reduced than
CO2 + H2O $ H2CO3 sulphides and carbonates.
Carbonic acid is formed.

4. Why oxides of highly reactive metals cannot be

reduced by carbon?
Ans : [CBSE 2015]
It is because highly reactive metals themselves are
good reducing agents, so they can’t be reduced by
carbon.

5. Give reason why: Electric wires are coated with plastic.

Ans : [CBSE 2015, 2014]
Plastic is a non-conductor of electricity, therefore
electric wires are coated with plastic.

6. Give composition of the alloy: brass and bronze.

13. From amongst the metal, sodium, calcium, aluminium,
Ans : [CBSE 2014]
copper and magnesium, name the metal:
Brass is made up of Cu and Zn. Bronze is made up of a. which reacts with water only on boiling.
Cu and Sn. b. another one which does not react even with steam.
7. What is the formula of rust? Ans : [CBSE 2013]
Ans : [CBSE 2014] a. Mg,
b. Cu
Rust is hydrated ferric oxide, Fe 2 O 3 $ xH 2 O .
14. Name any one metal which reacts neither with cold
8. An alloy has low melting point and is therefore water nor with hot water but reacts with heated
used for electrical fuse. Name the alloy and write its steam to produce hydrogen gas.
constituents.
Ans : [CBSE 2013]
Ans : [CBSE 2014]
Iron (Fe) :
Solder is an alloy. It is made up lead and tin. Heat
3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
9. Name one metal and one non-metal in liquid state at
15. Name the metals Which have low melting point. 4Al(s) + 3O2(g)
Heat
2Al2O3(S)
Aluminium oxide
Ans : [CBSE 2012, 2011]
Gallium and Caesium. 26. A non-metal X exists in two different forms V and Z.
Y is the hardest known natural substance, whereas Z
16. Name a non-metal which is lustrous whereas a metal is a good conductor of electricity. Identify X, Y and Z.
which is non-lustrous.
Ans : [CBSE 2011]
Ans : [CBSE 2012, 2011]
X is Carbon, Y is Diamond, Z is Graphite.
Iodine is a lustrous non-metal, Lead is a non-lustrous
metal. 27. Why does calcium float in water?
Ans : [CBSE 2011]
17. Choose the amphoteric oxide amongst the following:
Na2O, ZnO, Al2O3, CO2, H2O Calcium form hydrogen gas on reaction with water,
Ans : [CBSE 2012] bubbles of hydrogen gas sticks to the calcium metal
and that is why calcium floats in water.
ZnO and Al2O3 are amphoteric oxides. Ca(s) + 2H2O(l) $ Ca(OH)2(aq) + H2(g)
18. A green layer is gradually formed on copper plate 28. Which gas is liberated when a metal reacts with an
when left exposed to air for a week in a bathroom. acid? How will you test this gas?
What could this green substance be?
Ans : [CBSE 20111
Ans : [CBSE 2012]
Hydrogen gas is formed.
CuCO3.Cu(OH)2, Basic copper carbonate. Bring a burning splinter near the gas, it will burn with
‘pop’ sound.
19. Why do ionic compounds have high melting point?
Ans : [CBSE 2012] 29. An element ‘A’ form two oxides AO and AO2. The
It is due to strong forces of attraction between oxide AO is neutral whereas the oxide AO2 is acidic
positively charged and negatively charged ions. in nature. Would you call element ‘A’ a metal or a
non-metal?
20. Define metallurgy. Ans : [CBSE 2011]
Ans : [CBSE 2012] The element is carbon which is a non- metal. CO is
Metallurgy. All the processes involved in the extraction neutral and CO2 is acidic in nature.
of metals from its ore is called metallurgy.
30. Why do silver ornaments lose their shine when kept in
21. What kind of compounds are called Ionic compounds? open air for sometime?
Ans : [CBSE 2012] Ans : [CBSE 2011]
Those compounds which are formed between metals It is because Ag reacts with H2S present in the
and non-metals by transfer of electrons e.g., NaCl, atmosphere to form Ag2S due to which it loses its
KCl etc. shine.

22. How are ionic compounds formed? 31. Why do we use copper and aluminium wire for
Ans : [CBSE 2012] transmission of electric current?
Ans : [CBSE 2011]
Gallium has a melting point 303 K, it melts on palm.
Copper and aluminium are ductile and good
23. It nature, aluminium is found in combined state conductors of electricity, therefore they are used in
whereas silver/gold are found in free state. Give transmission wires.
reason.
Ans : [CBSE 2012, 2010, 2011] 32. Why do we use copper and aluminium wire for the
transmission of electric current?
Aluminium is reactive metal, therefore it is found in
Ans : [CBSE 2011]
combined state whereas silver/gold are less reactive
(noble) metals and so are found in free state. It is has 4 to 8 valence electrons, it is a non-metal.
Exception is hydrogen which has 1 valence electron
24. Why do ionic compounds conduct electricity in molten and He which has 2 valence electrons, but these are
state and not in solid state? non- metals.
Ans : [CBSE 2010,2012]
33. Name two metals which are found in nature in free
Ionic compounds do not conduct electricity in solid state.
state because ions are not free to move. In molten
Ans : [CBSE 2011]
state, ions are free to move.
Gold and silver are found in free state.
25. Write a balanced chemical equation for the reaction:
Aluminium when heated in air. Write the name of the 34. Why do we apply paint on iron grills?
product formed. Ans : [CBSE 2011]
Ans : [CBSE 2012] Iron grills are painted to prevent them from rusting.
35. Why does stainless steel not get rusted easily? c. Which is used to galvanise iron articles?
Ans : [CBSE 2010] d. Whose articles when exposed to air forms a black
coating?
Stainless steel is an alloy of Fe, C, Cr and Ni, therefore
it does not get rusted. Ans : [CBSE 2016]
a. Carbon makes it hard and strong. Tungsten also
36. Why do we use gold and platinum metals in jewellery? makes it hard and strong.
Ans : [CBSE 2010] b. Mercury is alloyed with metals to form amalgam.
Gold and Platinum are lustrous metals and do hot c. Zinc metal is used for coating over iron metal to
react with substances present in the atmosphere, galvanise iron.
therefore remain lustrous for a long time. d. Silver articles acquire black coating when left
exposed to the atmosphere.
37. Which property makes solder alloy suitable for welding
electric wires? 45. Which of the following listed metals can displace zinc
from its salt solution? Give reason for your answer
Ans : [CBSE 2010]
with a chemical equation:
Its melting point is low which makes solder suitable Copper, Lead, Magnesium, Silver
for welding. Ans : [CBSE 2016]
38. What is the valency of silicon with atomic number 14? Magnesium can displace zinc from zinc salt solution
Ans : [CBSE 2010] because Mg is more reactive than zinc:
Mg(s) + ZnSO4(aq) $ MgSO4(aq) + Zn(s)
Si (2,8,4): Its valency is 4 because it can share four
electrons to become stable. 46. The reaction of metal X with Fe2O3 is highly exothermic
and is used to join railway tracks. Identify metal X.
39. What is the valency of phosphorus with atomic
Write the chemical equation for the reaction.
number 15?
Ans : [CBSE 2016]
Ans : [CBSE 2010]
X is Al.
P (2, 8, 5): Its valency is 3 because it can gain three 2Al + Fe2O3 $ Al2O3 + 2Fe
electrons to become stable.
47. (a) In electrolytic refining of impure copper metal,
40. What is the valency of an element with atomic number
what are used as cathode and anode?
35? (b) Show the formation of HgCl2 from magnesium
Ans : [CBSE 2010] and chlorine atoms.
Br(35) (2, 8, 18, 7): Its valency is equal to 1 because Ans : [CBSE 2016]
it can gain one electron to become stable. (a) Pure copper is used as the cathode, impure copper
41. Arrange the following metals in decreasing order of is used as the anode.
reactivity are Na, K, Cu, Ag
(b)
Ans : [CBSE 2009]
K > Na > Cu > Ag is the decreasing order of reactivity. 48. Write one example of each of
a. a metal which is so soft, that it can be cut with a
42. Which of the following two metals will melt at body
knife and a non-metal which is the hardest known
temperature (37°C): Gallium, Magnesium, Caesium,
substance.
Aluminium?
b. a metal and a non-metal which exist as liquid at
Ans : [CBSE 2008(C)] room temperature.
Gallium and Caesium will melt at the body Ans : [CBSE 2015]
temperature.
a. Sodium is so soft that it can be easily cut with a
43. Show the electronic transfer in formation of MgCl2 knife.
from its elements. b. Diamond is the allotrope of carbon, which is the
Ans : [CBSE 2008] hardest known substance and a non-metal.
c. Mercury is a metal and Bromine is a non-
metal which are found in liquid state at room
temperature.

49. Mention the name of metals for the following:

a. Two metals which are alloyed with iron to make
TWO MARKS QUESTIONS stainless steel.
b. Two metals which are used to make jewellery.
Ans : [CBSE 2015]
44. Name a metal/non-metal
a. Which makes iron hard and strong? a. Nickel and chromium.
b. Which is alloyed with other metal to make b. Gold and platinum
amalgam?
50. Why is sodium chloride soluble in water but not in
 kerosene? b. Electrical wires are made up of copper.
Ans : [CBSE 2015] Ans : [CBSE 2014,2013]
Sodium chloride is the ionic compound and it form a. Metals are sonorous i.e., produce sound when
ions in water, therefore it is soluble in water whereas struck with a hard substance.
kerosene is a non-polar covalent compound, NaCl does b. Copper is a good conductor of electricity and is
not form ions in kerosene, therefore, it is insoluble in highly ductile.
it.
56. Out of the two metals P and Q, P is less reactive than
51. a. Why do aluminium sheets not corrode easily? Q. Suggest an activity to arrange these metals in the
b. Why is copper vessel corroded with a green order of decreasing reactivity. Support your answer
coating in rainy season? with a suitable chemical equation.
Ans : [CBSE 2015] Ans : [CBSE 2014]
a. Aluminium sheets are covered with an oxide layer Add Q in the salt solution of P. If Q is able to displace
which makes it passive. P’ from its salt solution, then it shows P is less reactive
b. It is due to the formation of basic copper than Q
carbonate, CuCO3.Cu(OH)2. Q + PR $ QR + P

52. A copper plate was dipped into a solution of silver 57. Define alloy. How an is alloy prepared?
nitrate. After sometime a black layer was observed on Ans : [CBSE 2014]
the surface of copper plate. State the reason for it and
Alloy is an homogeneous mixture of two or more
write chemical equation for the reaction involved.
metals. One of them can be a non-metal also. Alloys
Ans : [CBSE 2015] are made by melting two metals together and then
Copper is more reactive than Ag, therefore it can cooling it.
displace Ag from AgNO3 solution:
Cu(s) + 2AgNO3(aq) $ Cu(NO3)2(aq) + 2Ag(s) 58. In one of the methods of rust prevention, iron is not
coated with anything. Name that method and define
53. Give reason: it.
a. Carbonate and sulphide ores are usually converted Ans : [CBSE 2014]
into oxides during the process of extraction of
The method is alloy formation, by adding a suitable
metals.
metal or a non-metal.
b. Ionic compounds generally have high melting
point. Alloy is. a homogeneous mixture of two or more
c. Hydrogen is not a metal but has been assigned a metals. One of them can be a non- metal also. This
place in the reactivity services of metals. process is called alloying.
d. The galvanised iron article is protected against
rusting even if the zinc layer is broken. 59. Give reasons for the following:
a. Platinum, gold and silver are used for making
Ans : [CBSE 2015]
jewellery.
a. It is easier to reduce an oxide than sulphide and b. Sodium, potassium and lithium are stored under
carbonate ores. kerosene oil.
b. It is due to strong forces of attraction between c. Aluminium is highly reactive metal but still used
positive and negative ions. for making cooking utensils.
c. Hydrogen form H+ ions like metals, therefore it is d. Carbonate and sulphide ores are usually converted
included in the activity series. into oxides during the process of extraction.
d. Zinc is more reactive than iron, therefore it will Ans : [CBSE 2013, 2014]
get easily oxidised in preference to Fe and hence
protect iron from rusting even if zinc coating is a. It is because they are lustrous metals.
broken. b. These are highly reactive metals.
c. It forms an oxide layer on its surface which makes
54. A compound Z is formed by transfer of electrons from it passive.
the metal X to a non-metal Y, Identify the type of d. It is easier to reduce a metal oxide than sulphides
bond formed in the compound. List three properties and carbonates.
of compound formed by such type of bonds.
60. What happens to potassium and sodium if they are
Ans : [CBSE 2014]
kept in open? Why are they 3 immersed in kerosene
The bond formed is ionic bond: oil?
a. The compound will have high melting and boiling Ans : [CBSE 2013]
point.
b. It will be soluble in water. Potassium and Sodium if kept in open, can catch the
c. It will conduct electricity in molten state as well presence of moisture.
as in aqueous solution. They are immersed in kerosene so that they do
not react with air and H2O present in the atmosphere.
55. Give reason for the following:
a. School bells are made up of metals. 61. Why hydrogen gas is not evolved when a metal reacts
 with nitric acid? Molecular weight of NaOH = 40 g mol-1. Y is NaOH
Ans : [CBSE 2013] and Z is H2 gas which easily catches fire.
Nitric acid is an oxidising agent, therefore H2(g) is not 68. Name the following:
evolved on reaction with metal. Dilute HNO3 mostly a. A metal which is preserved in kerosene.
gets reduced to NO in this process. b. A lustrous coloured non-metal.
c. A metal which melts when kept on palm.
62. Why is iron galvanised with zinc? Can it be galvanised
d. A metal which is a poor conductor of heat.
with copper? If not, why?
Ans : [CBSE 2013, 2012]
Ans : [CBSE 2013]
a. Sodium or Potassium
Iron is galvanised by zinc because zinc is more reactive
b. Iodine
than Fe. Iron cannot be galvanised by copper because
c. Gallium
copper is less reactive than iron and therefore iron
d. Lead
itself gets corroded when coated with copper.
69. Define the term alloy. Write the constituents of
63. Differentiate between roasting and calcination giving
Bronze.
examples.
Ans : [CBSE 2013]
Ans : [CBSE 2013]
Alloy is a homogeneous mixture of two or more metals.
Roasting Calcination One of them can be a non- metal also.

1. It is done in the It is done in the Alloys are made by melting two metals together
presence of oxygen. absence of oxygen. and then cooling it.

2. It is done with It is done with 70. Why do silver articles turn black and copper items
sulphide ores eg. carbonate ores e.g. turn green after sometime?
2ZnS + 3O 2 $ 2ZnO + 2SO 2 FeCO 3 Heat
FeO (s) + CO 2 (g) Ans : [CBSE 2013]
Silver turns black due to the formation of Ag2S, (Silver
sulphide). Copper turns green due to formation of
64. Name the ore of mercury. How mercury is extracted basic copper carbonate.
from its ore?
Ans : [CBSE 2013] 71. Give reasons for the following:
a. Iron grills are frequently painted.
Cinnabar (HgS) is the ore of mercury.
b. Gold ornaments retain their lustre even after
Roasting:
several years of use.
HgS(s) + O2(g) $ 2Hg(l) + SO2(g)
Cinnabar, on roasting gives Mercury and sulphur Ans : [CBSE 2013]
dioxide. Mercury can be purified by distillation a. It is done to prevent them from rusting.
process. b. Gold is least reactive, therefore it remains lustrous
even after several years.
65. How is copper obtained from Cu2S? Give reactions.
Ans : [CBSE 2013] 72. Give reasons for the following:
a. Aluminium oxide is considered has amphoteric
a. Roasting:
oxide.
Cu2S(s) + 3O2(g) $ 2Cu2O(s) + SO2(g)
b. Ionic compounds conduct electricity in molten
b. Self-Reduction:
Heat state.
Cu2S(s) + 2Cu2O(s) 6Cu(s) + SO2(g)
Ans : [CBSE 2012]
66. Explain, why calcium metal after reacting with water a. Al2O3 reacts with acids as well as bases, therefore
starts floating on its surface. Write the chemical it is regarded as amphoteric oxide.
equation for the reaction. b. In molten state, ions are free to move, therefore it
Ans : [CBSE 2013, 2012] conducts electricity.
Calcium reacts with water to form Ca(OH)2 and H2
73. How do properties of iron change when
gas.
a. a small quantity of carbon is mixed in it?
Ca(s) + 2H2O(l) $ Ca(OH)2(aq) + H2(g)
b. nickel and chromium are mixed in it?
The bubbles of hydrogen gas sticks to the surface of
calcium and therefore it floats over water. Ans : [CBSE 2012]
a. It becomes hard and does not get rusted.
67. When a metal X is reacted with cold water, it gives b. It becomes lustrous and malleable and so it does
a basic compound Y with molecular formula XOH not get rusted.
(Molecular mass 40) and liberates a gas Z which easily
catches fire. Identify X, Y, Z. 74. You must have seen tarnished copper vessels being
Ans : [CBSE 2013, 2012] cleaned with lemon or tamarind juice. Explain why
these sour substances are effective in cleaning the
X is Na (Sodium).
vessels.
2Na(s) + 2H2O(l) $ 2NaOH(aq) + H2(s)
(Cold) Ans : [CBSE 2012]
 Copper vessel coated with a green layer of CuCO3. and then cooling the mould of two metals being mixed
Cu(OH)2 which reacts with acid present in lemon or that forms the alloy.
tamarind juice and get removed it. Some substances Solder is an alloy of lead and tin. It has low melting
contain acids which react with basic substances to point, therefore it is used for welding purposes.
form soluble salt which can be easily removed.
82. Using the electronic configuration, explain how
75. Name two metals which can be used to reduce metal
magnesium atom combines with oxygen atom to form
oxides to metals. magnesium oxide by transfer of electrons.
Ans : [CBSE 2012] Ans : [CBSE 2011]
Aluminium and Magnesium
2Al + Fe2O3 $ Al2O3 + 2Fe
3Mg + Fe2O3 $ 3MgO + 2Fe

76. Write four important purposes of making alloys.

Ans : [CBSE 2011]
a. It is done to increase the hardness of the substance.
83. Write chemical equations that shows aluminium oxide
b. It is done so as to increase the resistance towards
corrosion. reacts with acid as well base.
c. It helps to modify reactivity. Ans : [CBSE 2011]
d. It lowers the melting point. Al2O3 + 2NaOH $ 2NaAlO2 + H2O
Al2O3 + 3H2SO4 $ Al2(SO4)3 + 3H2O
77. State four general properties of ionic compounds.
Ans : [CBSE 2011] 84. Why is carbon not used for reducing aluminium oxide
a. They are soluble in water. to obtain Al?
[CBSE 2010]
b. They are hard but brittle solids.
or
c. They conduct electricity in solid state and in their
Metals placed high in reactivity series cannot be
aqueous solution.
obtained from their compounds by heating with
d. They have high melting and boiling points.
carbon?
78. The way, metals like sodium, magnesium and iron Ans : [CBSE 2011]
react with air and water is an indication of their It is because Al itself is a strong reducing agent,
relative positions in the ‘reactivity series’. Is this therefore it cannot be reduced by carbon.
statement true? Justify your answer with example.
Ans : [CBSE 2011] 85. A metal A which is used in thermite process, when
heated with oxygen gives an oxide B which is
Yes, Na reacts vigorously with cold water because it
amphoteric in nature. Identify A and B. Write down
is highly reactive. Magnesium reacts with hard water
the reactions of oxide of B with HCl and NaOH.
because it is less reactive than sodium. Iron reacts
only with steam because it is less reactive than Mg: Ans : [CBSE 2011]
2Na(s) + MgO(s) $ Na2O(s) + Mg A is Aluminium
3Mg + Fe2O3 $ 3MgO + 2Fe. 2Al + 3O2
Heat
Al2O3(S)
Al2O3 is an amphoteric oxide:
79. What are amphoteric oxides? Give two examples.
Al2O3 + 2NaOH $ 2NaAlO2 + H2O
Ans : [CBSE 2011] Al2O3 + 6HCl $2AlCl3 + 3H2O
Those oxides which react with acids as well as bases
are called amphoteric oxides e.g., Al2O3 and ZnO. 86. A substance X which is an oxide of metal is intensively
used in cement industry. The element is present in
80. X + YSO4 $ XSO4 + Y our bones also. On treatment with water, it forms a
Y + XSO4 $ No reaction solution which turns red litmus blue. Identify X and
Out of the two elements, X and Y, which is more also write the chemical reactions involved.
reactive and why? Ans : [CBSE 2011]
Ans : [CBSE 2011] X is calcium. Its oxide, CaO is used in cement industry.
X is more reactive than Y because it is displacing Y Calcium is also present in bones.
from its salt solution. Ca(s) + 2H2O(l) $ Ca(OH)2(aq) + H2(g)
Calcium hydroxide turns red litmus blue.
81. What is an alloy? State the constituents of solder.
Which property of solder makes it suitable for welding 87. Elements magnesium and oxygen respectively belong
electrical wires? to group 2 and group 16 of the Modern Periodic
Ans : [CBSE 2011] Table. If the atomic numbers of magnesium and
oxygen are 12 and 8 respectively, draw their electronic
Alloy is a homogeneous mixture of two or more metals. configurations and show the process of formation of
One of them can be a non- metal also. their compound by transfer of electrons.
Alloys are made by melting two metals together Ans : [CBSE 2010]
 series of metals help in predicting the relative
activity of various metals?
(b) Suggest different chemical processes used for
obtaining a metal from its oxides of metals in the
middle of the reactivity series and metals at the
top of the reactivity series. Support your answer
with one example each.
88. Write a balanced chemical equation for representing
Ans : [CBSE Sample Paper 2017-2018]
the chemical reaction between manganese dioxide
and aluminium powder. What happens if manganese (a) The series in which metals are arranged in
powder is heated with aluminium oxide? decreasing order of reactivity is called activity
Ans : [CBSE 2010] series of metals. The metal at the top is most
reactive, followed by less reactive metal and so on.
3MnO2 + 4A1 $ 2Al2O3 + 3Mn The metal at the bottom of activity series is least
No reaction will take place if manganese powder is reactive.
heated with Al2O3 because Mn is less reactive than Al. (b) Metals at the top of activity series are obtained
89. If a strip of aluminium with scratched clean surface
by electrolytic reduction e.g.,
is dipped into an aqueous solution of copper sulphate NaCl $ Na+ + Cl-
(Molten)
for a little time, the surface of the strip becomes At cathode :
brownish. What is the reason for this? Write the Na+ + e- $ Na
balanced chemical equation for this. At anode:
Ans : [CBSE 2010]
Cl- e- $ Cl
Aluminium is more reactive than copper, Cl + Cl $ Cl 2
2Al(s) + 3CuSO4(aq) $ Al2(SO4)3(aq) + 3Cu(s) Metals in the middle of the reactivity series are
90. Zinc does not evolve hydrogen gas on reacting with obtained by reduction with A1 e.g.,
HNO3. Why? Cr2O3 + 2Al $ Al2O3 + 2Cr
Ans : [CBSE 2010] 94. a. Write the steps involved in the extraction of pure
Dilute HNO3 is an oxidising agent, therefore it does metals in the middle of the activity series from
not liberate H2 with zinc. It oxidises N and liberates their carbonate ores.
NO gas (Nitrogen monoxide). b. How is copper extracted from its sulphide ore?
Explain the various steps supported by chemical
91. Write the electron dot structure for sodium and equations. Draw a labelled diagram for the
chlorine atoms. How do these atoms form a chemical electrolytic refining of copper
bond? Name the type of bond so formed. Why does a Ans : [CBSE 2016]
compound so formed have high melting point?
a. Following steps are involved in the
Ans : [CBSE Sample Paper 2008-2009]
i. Hydraulic washing: The carbonate ores is washed
, are electron dot structure of Na and chlorine with stream of water to remove earthly impurities.
atoms. Sodium can lose an electron and Cl gains that ii. Calcination: Carbonate ores is heated strongly in
electron and they form an ionic bond. the absence of air to form oxides e.g.,
Heat
ZnCO3 ZnO + CO2
iii. Reduction: ZnO is reduced with carbon to get Zn:
ZnO + C $ Zn + CO
iv. Electrolytic refining: Impure zinc is made as
anode, pure Zn is taken as cathode, acidified
It has high melting point due to strong forces of ZnSO4 of electrolyte’is used to get pure metal:
attraction between Na+ and Cl- ions. At anode: Zn $ Zn2+ + 2e-
(Impure)

92. Give reason for the following: At cathode: Zn2+ + 2e- $ Zn(s)
(Pure)
a. Metals can be given different shapes according to
b. Copper sulphite is concentrated by froth floation
our needs.
process.
b. Hydrogen is not evolved when a metal reacts with
i. 2Cu2S + 3O2 $ 2Cu2O + 2SO2
nitric acid.
ii. Reduction: Cu2S + 2Cu2O $ 6Cu + SO2
Ans : [CBSE 2008(C)] iii. Electrolytic refining:
a. Metals are malleable, therefore they can be given At cathode: Cu2+ + 2e- $ Cu
(pure)
different shapes.
At anode: Cu $ Cu2+ + 2e-
b. It is because HNO3(dil.) is a good oxidising agent. (Impure)

Acidified CuSO4 is taken as electrolyte.

THREE MARKS QUESTIONS

93. (a) What is reactivity series? How does the reactivity

 2. Set up the apparatus as shown in the diagram.
3. Plug the switch ON so that current starts flowing.
4. Record your observations.
5. Repeat the procedure with other metals.
Observation: The bulb glows with all metals.
Conclusion: Metals are good conductors of electricity.

95. Explain the following statements:

a. Most metal oxides are insoluble in water but some
of these dissolve in water. What are these oxides
and their solution in water called?
b. At ordinary temperature the surface of metals
such as magnesium, aluminium, zinc etc. is covered 99. a. What is an alloy? How is it prepared? Give two
with a thin layer. What is the composition of this examples of alloys.
layer? State its importance. b. Iron is not used in pure state. Give reason.
c. Some alkali metals can be cut with knife. Ans :
Ans : [CBSE 2016]
a. Alloy is a homogeneous mixture of two or more
a. These oxides are basic in nature and their solution metals. One of them can be a non-metal also.
are called alkalies. Alloys are made by melting two metals together
b. The composition of this layer is metal oxide. It and then cooling it. Example: Brass and Bronze
prevents the metal from corrosion. b. Iron gets rusted, therefore it is not used in pure
c. Sodium can be cut with a knife because it is a state.
very soft metal.
100. A metal P when exposed to moist air for a longer
96. Write one example of each of the following: period of time, loses its shining brown surface and
a. Most malleable and most ductile metal. attains a green coating; what has happened? Identify
b. The best conductor of heat and poorest conductor the metal, write the name and chemical formula of
of heat. green coloured compound. List two ways to prevent
c. ‘A metal with highest melting point and a metal this process.
with lowest melting point. Ans : [CBSE 2016]
Ans : [CBSE 2016]
It undergoes corrosion. The metal is copper.
a. Gold is most malleable and ductile. Chemical formula of green coloured compound is
b. Copper is the best conductor and lead is a poor CuCO3.Cu(OH)2
conductor of heat copper. a. It can be prevented by coating of tin over iron.
c. Tungsten has highest melting point, mercury has b. It can also be prevented by coating it with paint.
lowest melting point.
101. Name the constituent elements of alloys:
97. Aluminium oxide and zinc oxide react with both acids a. Brass,
and bases to produce salt and water. What are these b. Bronze,
oxides called? Write chemical equations in each case. c. Solder.
Ans : [CBSE 2016] Mention one use of each alloy.
These are called amphoteric oxides: Ans : [CBSE 2016]
Al2O3 + 2NaOH $ 2NaAlO2 + H2O a. Brass is made up Cu and Zn. It is used for making
ZnO + 2NaOH $ Na2ZnO2 + H2O decorative articles.
ZnO + 2HCl $ ZnCl2 + H2O b. Bronze is made up of Cu and Sn. It is used for
Al2O3 + 6HCl $ 2AlCl3 + 3H2O making statues, medals.
c. Solder it is an alloy of Pb and Sn. It is used for
98. Describe an activity to show that metals are good soldering purposes.
conductors of electricity.
Ans : [CBSE 2016] 102. Give reasons only:
a. We can store copper sulphate solution in a silver
Activity: To show metals are good conductors of
vessel but not silver nitrate solution in copper
electricity.
vessel.
1. Take copper wire and insert two clips with a
b. The reaction of zinc with dilute HNO3 does not
sample to be inserted between them, as shown in
produce H2 gas.
the diagram.
 c. Food cans are coated with tin rather than zinc. is malleable and ductile.
Ans : [CBSE 2016] c. Sulphur does not conduct electricity whereas
magnesium conducts electricity.
a. It is because copper is more reactive than silver,
it will displace Ag from AgNO3 solution. Thus 106. A metal forms an oxide having formula M2O3. It
we can’t store AgNO3 in a copper container but dissolves both in dilute sulphuric acid as well as dilute
CuSO4 can be stored in silver vessel as no reaction sodium hydroxide solution. Identify the metal and
will take place because silver is less reactive. write the equations for the reactions involved.
b. Dilute HNO3 is an oxidising agent. Ans : [CBSE 2015]
c. Tin is less reactive and less expensive than zinc.
The metal is Al. Its oxide is Al2O3.
103. Name a metal in each case: Al2O3 + 2NaOH $ NaAlO2 + H2O
a. It displaces hydrogen gas on reaction with nitric Al2O3 + 3H2SO4(aq) $ Al2(SO4)3(aq) + 3H2O(l)
acid.
b. It does react with any physical state of water. 107. State the conditions under which the following metals
c. It does not react with cold water or hot water, but react with water. Write chemical equation for its
reacts with steam. reaction with each: (a) Na (b) Mg (c) Fe
Ans : [CBSE 2015] Ans : [CBSE 2015]
a. Mg and Mn (a) Sodium metal reacts with cold water as:
b. Cu 2Na + 2H2O $ 2NaOH + H2
c. Iron (b) Magnesium reacts with hot water as:
Mg + 2H2O $ Mg(OH)2 + H2
104. Distinguish between the following: (c) Iron reacts with steam as:
a. Electrolytic reduction and electrolytic refining. 3Fe + 4H2O $ Fe3O4 + 4H2
b. Mineral and ore.
c. Alloys and amalgams 108. What is cinnabar? How is metal extracted from
cinnabar? Explain briefly.
Ans : [CBSE 2015]
Ans : [CBSE 2015]
Electrolytic reduction Electrolytic refining Cinnabar (HgS) is an ore of mercury.
Roasting: HgS(s) + O2(g) $ 2Hg(l) + SO2(g)
Metal is obtained by Metal is refined by
Cinnabar, on roasting gives Mercury and sulphur
electrolysis of molten taking impure metal as
dioxide. Mercury can be purified by the process of
ore. anode, pure metal as
distillation.
cathode and soluble salt
of metal as electrolyte 109. a Write the electron dot structure of Potassium (19)
and by passing electric and Chlorine (17).
current. b. Show the formation of KCl by transfer of electrons.
Mineral ore c. Name the ions present in the compound, KCl.
Naturally occurring Naturally occurring Ans : [CBSE 2015]
substances from substances from which a. and are electron dot structures.
which metal may or metal is extracted
may not be extracted profitably e.g., Bauxite b.
economically e.g., Mica. is an ore of Al.
Alloys amalgams
Homogeneous mixture of Homogenous mixture
two or more metals. One of mercury with any
of them can be a non- other metals e.g., zinc c. and ions are present in KCl.
metal also e.g., steel. amalagam. 110. a.Write the electron-dot structure of calcium and
sulphur.
105. State three reasons for the following facts: b. Show the formation of CaS by transfer of electrons.
a. Sulphur is a non-metal. c. Name the ions present in the compound, CaS.
b. Magnesium is a metal. Atomic number of Ca = 20, S = 16.
One of the reason must be supported with a chemical
Ans : [CBSE 2015]
equation.
Ans : [CBSE 2015] a. and
a. Sulphur is a non-metal because it reacts with O2 b.
to form SO2 which is an
acidic oxide: S + O2 $ SO2
Magnesium is a metal which reacts with O2 to
form basic oxide:
2Mg + O2 $ 2MgO c. and are present in CaS.
b. Sulphur is not malleable and ductile, magnesium
111. Give one most suitable word for the following Heat
statements: c. Cr2O3(s) + 2Al(s) Al2O3(s) + 2Cr(l)
a. Metal oxides which show basic as well as acidic
116. A, B and C are three elements which undergo chemical
behaviour.
reactions according to the following equations:
b. Some metals produce a sound on striking with a
A2O3 + 2B $ B2O3 + 2A ,
hard surface.
3CSO4 + 2B $ B2(SO4)3 + 3C
c. Iodine, shining non-metal.
3CO + 2A $ A2O3 + 3C
Ans : [CBSE 2015] a. Which element is most reactive?
a. Amploteric oxide, b. Which element is the least reactive?
b. Sonorous, c. What type of reactions is listed above?
c. Lustrous. Ans : [CBSE 2014]
112. State the property utilised in the following: a. B is most reactive.
a. Graphite in making electrodes. b. C is least reactive.
b. Electric wires are coated with polyvinyl chloride c. Displacement reactions.
(PVC) or rubber like materials.
117. List three properties of sodium in which it differs from
c. Metal alloys are used for making bells and strings
general physical properties of most metals.
of music instruments.
Ans : [CBSE 2014]
Ans : [CBSE 2015]
a. It is soft.
a. Graphite is a good conductor of electricity.
b. It has low melting and boiling point.
b. PVC is an insulator, protects us from electric
c. It is not malleable and ductile.
current.
c. Alloys are stronger and more sonorous than metals
and used for bells and musical instruments. They
do not get rusted.

113. Write chemical equations for the reactions taking

place when:
a. Iron reacts with steam.
b. Magnesium (Mg) reacts with dilute HCl.
c. Copper is heated in air.
Ans : [CBSE 2014]
Heat
a. 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
b. Mg(s) + 2HCl(dil.) $ MgCl2(aq) + H2(g)
c. 2Cu(s) + O2(g) $ 2CuO(s)

114. How metals can be differentiated from non-metals on

118. Describe ionic compounds on the basis of following
the basis of any of it three chemical roperties?
properties:
Ans : [CBSE 2014] a. Strong forces of attraction between positive and
negative ions.
Metal Non-metals b. Solubility of compounds in water.
1. Metallic oxides are Non-metallic oxides are c. Electrical conductivity.
basic in nature. acidic in nature Ans : [CBSE 2014]
2. Most of metals Non-metals do not lib- a. They have high melting and boiling points.
liberate H2 gas with erate H2 gas with dilute b. They are soluble in water.
dilute acids. acids. c. They conduct electricity in molten state and in
aqueous solution.
3. Metal hydroxides, Non metallic oxides form
bases turn red acid in aqueous solution, 119. a.Name the metal which does not stick to the glass,
litmus blue. which turns blue litmus b. Name a metal which is commonly used in thermite
red. welding.
c. What is the nature of Zinc oxide?
115. Write chemical equations for the reactions taking Ans : [CBSE 2014]
place when:
a. Iron is strongly heated with air. a. Mercury.
b. Lead carbonate is calcined. b. Aluminium displaces molten iron from Fe2O3
c. Chromium oxide (Cr2O3) is heated with aluminium which is used in thermite reaction for welding
powder. purpose.
c. It is amphoteric.
Ans : [CBSE 2014]
a. 3Fe(s) + 2O2(g)
Heat
Fe3O4(s) 120. a.Define the term ‘anode mud’. Name an electrode
made of pure metal.
Heat
b. PbCO3(s) PbO(s) + CO2(g) b. Give the reactions taking place at cathode and
 anode during the electrolytic refining of copper. The process in which iron reacts with oxygen in the
Ans : [CBSE 2014] presence of moisture to form brown layer on its surface
is called rusting.
a. The impurities left behind at anode after impure
copper metal undergoes electrolytic refining is
called anode mud.
b. At anode:
Cu (s) $ Cu2+ (aq) + 2e-
(impure)
At cathode:
Cu2+ (aq) + 2e- $ Cu (s)
(Pure)

121. Name two metals which are purified by electrolytic

refining. Mention the cathode, anode and electrolyte
used in the refining process. At which electrode would
the pure metal be deposited?
Ans : [CBSE 2014]
Cu, Zn, Al can be purified by electrolytic refining
method:
At cathode, pure metal is deposited. Cathode is made
up of pure metal. Anode is made up of impure metal.
Soluble salt of metal is used as electrolyte.
126. a.Show the formation of Na2O by transfer of
122. Write the balanced chemical equation in each case: electrons between the combining atoms.
a. Mg metal is reacted with very, little amount of b. Why are ionic compounds usually hard?
dilute HNO3. c. How is it that ionic compound in the solid state
b. Aluminium powder is added to Fe2Og. do not conduct electricity but they do so in the
c. Zinc sulphide is roasted. molten state?
Ans : [CBSE 2014] Ans : [CBSE 2012]
a. Mg (s) + 2HNO 3 (S) $ Mg (NO 3) 2 (aq) + H 2
a.
3Mg (s) + dil.HNO 3 $ Mg (NO 3) 2 + 2NO + 4H 2 O
b. 2A1 + Fe2O3 $ Al2O3 + 2Fe
c. 2ZnS + 3O2 $ 2ZnO + 2SO2

123. Suggest a method of reduction for the following metals

during metallurgical processes:
a. Metal A which is one of the last, second or at the b. Ionic compounds are hard due to strong forces of
third position in the reactivity series. attraction between oppositely charged ions.
b. Metal B which gives vigorous reaction even with c. In solid state, ions are not free to move but in
water and air. molten state, ions are free to move.
c. Metal C which is kept in the middle of the activity
series. 127. Define the terms: (a) mineral, (b) ore and (c) gangue
Ans : [CBSE 2013] Ans : [CBSE 2012]
a. Reduction with carbon. a. Mineral: It is a naturally occurring substance
b. Electrolytic reduction. from which metal may or may not be extracted
c. Reduction with Al. economically e.g., Mica.
b. Ores: These are naturally occurring substances
124. a.Explain the formation of ionic compound CaO from which metal can be extracted profitably e.g.,
with its electron dot structure. Atomic number of Haematite.
Ca = 20, O = 8. c. Gangue: The impurities present in the ore is called
b. Name the constituents of bronze. gangue e.g., SiO2.
Ans : [CBSE 2012]
128. An ore on heating in air produces sulphur dioxide.
a. Which process would you suggest for its concentration?
Describe briefly any two steps involved in the
conversion of the concentrated ore into the related
metal.
Ans : [CBSE 2009]
b. Bronze is made up of Copper and Tin. It is concentrated by using froth floatation process.
a. Roasting: The ore is heated in the presence of
125. What is meant by rusting? With labelled diagrams,
oxygen to form oxide e.g.,
describe an activity to find out the conditions in
2ZnS + 3O2 $ 2ZnO + SO2
which rusting takes place.
b. Reduction: ZnS is reduced by ZnO to get Zn and
Ans : [CBSE 2012] SO2. Carbon can also be used to reduce ZnO to
 Zn:
ZnS + 2ZnO $ 3Zn + SO2
ZnO + C $ Zn + CO

129. Observe the two test tubes A and B as shown in b. It is an ionic compound.
the diagram given below and answer the following 1. It is soluble in water.
questions : 2. It conducts electricity in molten state and in
aqueous solution.
3. It is a hard solid.

132. a.What type of ores are calcined? Illustrate with

suitable examples.
b. In what form calcined ore is obtained and how it
can be reduced? Give chemical equation for the
reduction process involved for the example given
by you.
c. Name any two metals used as reducing agents
by displacing metals of low reactivity from their
compounds.
a. In which test tube will the reaction take place?
b. Write a balanced chemical equation for the Ans : [CBSE 2015]
reaction. a. Carbonate ores are calcined e.g.,
Heat
c. Name the type of reaction. CuCO3(s) CuO(s) + CO2(g)
Ans : [CBSE 2008(C)] b. It is obtained in oxide form. It is reduced by using
a suitable reducing agent e.g.,
a. In the first test tube reaction will take place. Heat
b. Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s) CuO(s) + C Cu(s) + CO(g)
c. Displacement reaction. c. Al and Mg.

133. a.An ore on treatment with dilute hydrochloric acid

FIVE MARKS QUESTIONS produces brisk effervescence. What kind of ore is
this? What steps will be required to obtain metal
from the enriched ore?
130. a.Define corrosion. b. Copper coin is kept immersed in silver nitrate
b. What is corrosion of iron called? solution for sometime. What change .will take
c. How will you recognise the phenomena of corrosion place in the coin and in the colour of the solution?
of silver? Write a balanced chemical equation for the
d. Why corrosion of iron metal is a serious problem? reaction.
e. How can we prevent corrosion of iron? Ans : [CBSE 2014]
Ans : [CBSE 2016] a. It is a carbonate ore.
a. Corrosion: The process in which a metal react (i) Hydraulic washing, (ii) Calcination,
with substances present in atmosphere to form (iii) Reduction, (iv) Refining.
surface compounds is called corrosion. b. The solution will become blue in colour, blackish
b. Corrosion of iron is called rusting. silver metal will get deposited:
c. It turns black on corrosion due to the formation Cu ^ s h + 2AgNO 3 ^aqh $ Cu ^NO 3h2 ^aqh + 2Ag ^ s h
of Ag2S.
d. It weakens bridges and materials and a lot of iron 134. a.Define activity series of metals. Arrange the
gets wasted every year. metals: gold, copper, iron and magnesium in the
e. We can prevent corrosion of iron by order of their increasing reactivity.
1. Painting, b. What will you observe when:
2. Oiling and greasing, (1) Some zinc pieces are placed in copper sulphate
3. Galvanisation, solution.
4. By forming its alloys. (2) Some silver pieces are placed into green
coloured ferrous sulphate solution.
131. a.Write electron dot diagrams of chlorine (At. No. Ans : [CBSE 2013]
17) and calcium (At. No. 20). Show the formation
of calcium chloride by transfer of electrons. a. The series in which metals are arranged in
b. Identify the nature of the above compound decreasing order of reactivity is called activity
and explain three physical properties of such a series of metals. The metal at the top is most
compound. reactive, followed by less reactive metal and so on.
The metal at the bottom is least reactive.
Ans : [CBSE 2015] Au < Cu < Fe < Mg is the increasing order of
a. reactivity.
b. (1) The solution will become colourless, reddish
brown copper metal will get deposited:
Zn(s) + CuSO4(aq) $ ZnSO4(aq) + Cu(s)
 (2) No reaction will take place because Ag is less 2Al(s) + Fe2O3(s)
Heat
Al2O3(l) + Fe(l)
reactive than Fe. A B D (Iron)
C

135. A metal (E) is stored under kerosene oil. When a small This reaction need heat to start but it is highly
piece of it is left open in air, it catches fire. When exothermic.
the product formed is dissolved in water, it turns red This reaction belongs to the category of:
litmus blue. (1) Displacement reaction,
a. Name the metal (E). (2) Redox reaction.
b. Write the chemical equation for the reaction 137. Four metals A, B, C and D are added to the following
when it is exposed to air and when the product is aqueous solutions one by one. The observations made
dissolved in water. are tabulated below:
c. Explain the process by which metal is obtained
from its molten chloride. Iron (II) Copper (II) Zinc Silver nitrate
Ans : [CBSE 2012,2011] sulphate sulphate sulphate
A No Reaction Reddish Brown .......... ..........
a. E is sodium metal. Deposit
b. 2Na + 2H2O $ 2NaOH + H2
B Grey Deposit .......... No Reaction ..........
H2 gas will catch fire.
NaOH turns red litmus blue. C No Reaction No Reaction No Reaction White Shining
4Na(s) + O2(s) $ 2Na2O(s) Deposit
Na2O + H2O(aq) $ 2NaOH(aq) D No Reaction No Reaction No Reaction No Reaction
c. It is obtained by electrolytic reduction e.g., ‘Na’
metal is obtained by electrolysis of molten NaCl: Answer the following questions based on the above
NaCl
Electrolysis
N+ + Cl- observations:
Molten a. Which is the most active metal and why?
At cathode: Na+ + e- $ Na b. What would be observed if B is added to copper
At anode: Cl- $ Cl + e- (II) sulphate solution and why?
Cl + Cl $ Cl2 c. Arrange the metals A, B, C and D in order of
increasing reactivity.
136. a.Write two differences between calcination and d. Container of which metal can be used to store
roasting. [CBSE 2012] both zinc sulphate solution as well as silver nitrate
b. ‘No reaction takes place when granules of a solid solution?
‘A’ is mixed with a powder of solid ‘B’. However e. Which of the above solutions can be easily stored
when the mixture is heated, a reaction starts with in a container made up of any of these metals?
the evolution of much heat. Product ‘C’ of the
Ans : [CBSE Sample Paper 2009]
reaction settles down as a liquid metal and a solid
product ‘D’ keeps on floating over the liquid ‘C’. a. B is the most reactive because it displaces Fe. It
This reaction is sometimes used for making metals will displaces Fe. It will displace Cu as well as Ag
for ready use in odd places. also.
a. Based on this information, make assumptions b. B will displace copper from CuSO4 solution
about metals ‘A’ and ‘B’ and corresponding because it is more reactive than Cu.
deductions about ‘C’ and ‘D’ and write a balanced c. D is least reactive and D<C<A<B is the
chemical equation for the reaction. Include in increasing order of reactivity.
the chemical equation about the physical states d. Container of metal D can be used to store both
of the reactants and products, need for heating ZnSO4 and AgNO3.
for starting the reaction and the reaction being e. Zinc sulphate solution can be stored in container
exothermic. made up any of the metals A, B, C, D because none
b. Name two types of chemical reactions to which of them could displace zinc from zinc sulphate as
this reaction can belong to. these are less reactive than zinc.
Ans : [CBSE 2012]
a. Differences between calcination and roasting.

Roasting Calcination
1. It is done in the It is done in the
presence of oxygen. absence of oxygen.
2. It is done with It is done with
sulphide ores eg. carbonate ores e.g.
Heat
2ZnS + 3O2 FeCO3
$ FeO(s) +
2ZnO + CO2(g)
2SO2
b. A is Al, B is Fe2O3, C is molten Iron, D is Al2O3
(Molten)
Chap 5 : Periodic Classification of Elements www.cbse.online

CHAPTER 5
Periodic Classification of Elements

ONE MARK QUESTIONS A(12): 2, 8, 2, B(18): 2, 8,8, C(20): 2, 8, 8, 2

A and C belong to the same group because they have
same number of valence electrons.
1. An element has atomic number 17. To which group
9. Why are H, Li, Na and K placed in group-1?
and period does it belong to?
Ans : [CBSE 2015]
Ans : [CBSE 2016]
It is because they have one valence electron.
X(17): 2,8,7 is the electronic configuration. It has 7
valence electrons. It belongs to 17th group and 3rd 10. Write the number of horizontal rows in the modern
period. periodic table. What are these rows called?
2. Out of Li and K, which will have stronger metallic Ans : [CBSE 2014]
character and why? There are 7 horizontal rows in the modern periodic
Ans : [CBSE 2016] Table. These rows are called periods.
K will have more metallic character because it can
lose electrons easily due to its bigger atomic size and
less effective nuclear charge.

3. Find the atomic number of the element whose

electronic configuration is 2, 8, 5.
Ans : [CBSE 2016)
Atomic number = 2 + 8 + 5 = 15.

4. An element A has atomic number 16. To which group

and period does it belong to?
Ans : [CBSE 2016]
A(16) has electronic configuration: 2, 8, 6. It has 6
valence electrons and three shells. It belong to Group
16, 3rd period. 11. Write one difference between Group 1 and Group 2
elements?
5. Write two reasons responsible for the late discovery of
Ans : [CBSE 2014]
noble gases.
Ans : [CBSE 2015] Group 1 elements has 1 valence electron whereas
group 2 elements has 2 valence electrons.
a. They are inert i.e., least reactive.
b. They are less abundant in nature except Argon. 12. Write the atomic numbers of two elements X and Y
having electronic configurations 2, 8, 2 and 2, 8, 6,
6. How many vertical columns are there in the modern respectively.
periodic table and what are they called?
Ans : [CBSE 2014]
Ans : [CBSE 2015, 2014]
X = 2 + 8 + 2 = 12
There are 18 vertical columns in Modern Periodic Y = 2 + 8 + 6 = 16
Table. They are called groups.
13. State the modern periodic law of classification of
7. List any two properties of elements belonging to the elements.
first group of modem periodic table.
Ans : [CBSE 2014, 2013]
Ans : [CBSE 2015, 2014]
Modern Periodic Law: It states ‘properties of elements
a. They have 1 valence electron. are a periodic function of their atomic number’.
b. Their valency is equal to 1.
14. Out of the three elements P, Q and R having atomic
8. The atomic number of three elements A, B and C are numbers 11, 17 and 19 respectively, which two elements
12, 18 and 20 respectively. State giving reason, which will show similar properties and why?
two elements will show similar properties.
Ans : [CBSE 2014]
Ans : [CBSE 2015, 2014]
P(11): 2, 8, 1; Q(17): 2, 8, 7; R(19): 2, 8, 8, 1
 P and R will show similar chemical properties because after the formation of Mendeleev’s periodic table.
they have the same number of valence electrons. Ans : [CBSE 2011]
15. Write the formula which is used to determine the Gallium and Germanium.
maximum number of electrons that a shell can
25. What is a metalloid? Name any two of them.
accommodate.
Ans : [CBSE 2011]
Ans : [CBSE 2014, 2013]
Metalloids are those elements which resembles both
2n2 , where n is the shell number.
with metals as well as non-metals e.g., Boron and
16. What would be the nature of oxides formed by the Silicon.
elements on the right side of periodic table?
26. Arrange the following metals in decreasing order of
Ans : [CBSE 2014] their atomic size:
On right hand side of the periodic table, most of them Ca, Mg, Ba, Be
are non-metals, therefore they form acidic oxides. Ans : [CBSE 2011]
17. Predict the maximum number of valence electrons Ba > Ca > Mg > Be is the decreasing order of atomic
possible for atoms in the first period of the periodic size.
table.
27. Why does atomic size decreases as we move from left
Ans : [CBSE 2014} to right along a period in a periodic table?
Maximum number of valence electrons in 1st period Ans : [CBSE 2011]
is 2.
It is because one proton and one electron is being
18. The electronic configuration of two elements X and Y added successively, therefore effective nuclear charge
are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic increases, atomic size decreases.
numbers of X and Y.
28. What is the valency of silicon with atomic number 14?
Ans : [CBSE 2013]
Ans : [CBSE 2010]
X = 2 + 8 + 7 = 17
Si(2, 8, 4), the number of valence electrons in Si is 4.
Y = 2 + 8 + 8 + 3 = 21
Therefore, its valency is 4.
19. The atomic numbers of three elements X, Y and Z are
29. What is the valency of phosphorus with atomic
3, 11 and 17 respectively. State giving reason which
number 15?
two elements will show similar properties.
Ans : [CBSE 2010]
Ans : [CBSE 2013]
P(2, 8, 5) has 5 valence electrons, therefore its valency
X= 2, 1
is equal to 3.
Y = 2,8, 1; Z = 2, 8, 7
X and Y will show similar properties due to same 30. What is the valency of an element with atomic number
number of valence electrons. 35?
20. Give reason why noble gases are placed in a separate Ans : [CBSE 2010]
group in the modern periodic table. Atomic number is 35, it has electronic configuration
Ans : [CBSE 2013] of 2, 8, 18, 7. It has 7 valence electrons, therefore its
valency is equal to 1.
It is because they have their outermost shell completely
filled and resemble with each other. 31. What were the criteria used by Mendeleev in creating
his periodic table?
21. Name any two pairs of elements which were adjusted
by Newlands in the same slot. Ans : [CBSE 2013]
Ans : [CBSE 2013] Increasing order of atomic mass and same formula of
oxides and hydrides.
(i) Co and Ni, (ii) Ce and La
32. Give the number of elements in 2nd and 5th period in
22. Define Newlands law of octaves.
the modern periodic table.
Ans : [CBSE 2013]
Ans : [CBSE 2013]
Newlands Law of Octaves: When elements are arranged
In 2nd period, there are 8 elements.
in increasing order of their atomic mass, every eighth
In 5th period, there are 18 elements.
element resembles with the first.
33. Lithium, Sodium and potassium form a Dobereiner’s
23. State Mendeleev’s periodic law.
triad. The atomic masses of lithium and potassium
Ans : [CBSE 2012] are 7 and 39 respectively. Predict the atomic mass of
Mendeleev’s Periodic Law: Properties of elements are sodium.
a periodic function of their atomic mass. Ans : [CBSE 2009C]
24. Name any two elements which were discovered later Atomic mass of Sodium
 Atomic mass of lithium Group 1 Group 2
+ Atomic mass of potassium
= Li(3): 2,1 Be(4): 2, 2
2
K(19):2,8,8,1 Mg (12): 2, 8, 2
Na = 7 + 39 = 46 = 23
2 2
Li and K are placed in group 1 due to same number of
34. Why was the system of classification of elements into valence electrons. In second group the atomic number
triads not found suitable? of first two elements will be 4 and 12 respectively.
Ans : [CBSE 2009(C)]
40. Calcium is an element with atomic number 20.
It is because all the elements discovered at that time
a. Will it be a metal/non-metal?
could not be classified as Dobereneire’s triads.
b. What will be its valency?
35. The formula of magnesium oxide is MgO. State the c. What would be the formula of its chloride?
formula of barium nitrate and barium sulphate, if d. Will it be smaller / larger than K?
barium belongs to same group as magnesium. Ans : [CBSE 2016]
Ans : [CBSE 2012] Ca(20): 2, 8, 8, 2
The valency of Mg is 2. The valency of Ba is also 2 a. It will be a metal.
as they belong to the same group. Formula of Barium b. Its valency is equal to 2.
nitrate is Ba(NO3)2, and that of Barium sulphate is c. CaCl2 is the formula of its chloride.
BaSO4. d. It will be smaller than K.

36. Which has larger atomic radius, K(19) or Ca(20)?

Ans : [CBSE 2016]
K has larger atomic radius than Ca.

37. Chlorine, Bromine and Iodine form Dobereiner’s

triads. The atomic mass of Cl and I are 35.5 and 126.9
respectively. Predict the atomic mass of Bromine.
Ans : [CBSE 2009]
Atomic Mass of Br
= Atomic mass of Cl + Atomic mass of I
2

= 35.5 + 126.9 = 162.4 = 81.2

2
Electronic configuration: X = 2, 8, 7 41. List the anomalies of Mendeleev’s periodic table which
It has 7 valence electrons. It belongs to group 17. were removed in Modem Periodic Table.
It has 3 shells, therefore it belongs to 3rd period. Ans : [CBSE 2016]
It can gain 1 electron to become stable, so its valency
is equal to 1. Co with higher atomic mass proceeds Ni with lower
atomic mass. It was solved because Co has lower
atomic number than Ni.
TWO MARKS QUESTIONS Isotopes should have been given different slots
due to different atomic mass, but it is not possible due
38. An element X has mass number 35 and the number of to same chemical properties. The problem was solved
its neutrons is 18. Identify the group number, period because isotopes have same atomic numbers.
and valency of element X’. 42. Choose from the following:
Ans : [CBSE Sample Paper 2017-2018, CBSE 2016] C, 8O, 10Ne, 11Na, 14S1
6
X has mass number 35, number of neutrons = 18
a. Elements that should be in the same period.
Atomic Number = 35 - 18 = 17
b. Elements that should be in the same group.
a. Electronic configuration: X = 2, 8, 7 It has 7
State the reason for your selection in each case.
valence electrons. It belongs to group 17.
b. It has 3 shells, therefore it belongs to 3rd period. Ans : [CBSE 2016,2012]
c. It can gain 1 electron to become stable, so its a. 6
C(2, 4), 8O(2, 6), 10Ne(2, 8) belong to the same
valency is equal to 1. period i.e., 2nd period and 11Na(2, 8, 1), 14Si(2, 8,
4) belongs to the same period i.e., 3rd period.
39. Why is lithium with atomic number 3 and potassium b. 6C(2,4) and 14Si(2,8,4) belongs to the same group
with atomic number 19 are placed in group one? What -14 due to same number of valence electrons,
will be atomic number of the first two elements in the which is equal to 4.
second group?
Ans : [CBSE 2016] 43. The elements X, Y and Z having atomic numbers 11,
7 and 6 respectively react with oxygen to form their
 oxides. 49. An element ‘X’ has atomic number 13.
a. Arrange these oxides in increasing order of their a. Write its electronic configuration.
basic nature. b. State the group to which ‘X’ belongs to.
b. Give reason for your answer. c. Is ‘X’ a metal or a non-metal?
Ans : [CBSE 2015] d. Write the formula of its bromide.
X(11) is sodium and it will form Na2O, Y(7) is Ans : [CBSE 2012]
Nitrogen that will form N2O5, Z(6) is carbon which a. X(13) : 2, 8, 3
will form CO2. b. It belongs to group 13.
a. N2O5 < CO2 < Na2O c. It is a metal.
b. It is because non-metallic character increases d. XBr3 is the formula of its bromide.
along a period, therefore basic character of oxides
decreases, and acidic nature increases from left to 50. State the modern periodic law for the classification of
right across the period. elements. How many (a) groups, (b) periods are there
in Modern Periodic Table?
44. a. Name the element with atomic number 17. Ans : [CBSE 2012]
b. To which period does it belong to?
Properties of elements are a periodic function of their
c. To which group does it belong to?
atomic numbers. There are 18 groups and 7 periods in
d. Write its electronic configuration.
modern periodic table.
Ans : [CBSE 2015,2014]
a. Chlorine (17): 2, 8, 7 51. An element M has atomic number 11.
b. It belongs to 3rd period. a. Write its electronic configuration.
c. It belongs to group 17. b. State the group to which M belongs to.
d. 2, 8, 7 is the electronic configuration of chlorine. c. Is M a metal or a non-metal?
d. Write the formula of its chloride.
45. a. Amongst the following elements identify the ones Ans : [CBSE 2012]
that would form anions:
a. 2, 8, 1
K, O, Na, F, Ca, Cl, Mg
b. M belongs to group 1.
b. Write the electronic configuration of the anions
c. It is a metal.
identified above.
d. MCI is the formula of its chloride.
Ans : [CBSE 2015, 2014]
O, F, Cl will form anions. 52. An element M has atomic number 12.
O2- (18): 2, 8 a. Write its electronic configuration.
F- (10): 2, 8 b. State the group to which M belongs to.
Cl- (18): 2, 8, 8 c. Is M a metal or a non-metal?
d. Write the formula of its oxide.
46. An element belongs to third period and second group Ans : [CBSE 2012]
of the periodic table:
a. 2, 8, 2,
a. State the number of valence electrons in it.
b. Group 2,
b. Is it a metal or a non-metal?
c. Metal,
c. Name the element.
d. MO is formula of its oxide.
d. Write the formula of its oxide.
Ans : [CBSE 2015, 2011] 53. How can the valency of an element be determined if
a. It has 2 valence electrons. its electronic configuration is known? What will be
b. It is a metal valency of an element with atomic number 9?
c. Magnesium. Ans : [CBSE2012,2011]
d. MgO is the formula of its oxide. Valency=Number of valence electrons in case of
metals and metalloids. It is also equal to 8 — Number
47. Write the trend of atomic size and metallic character
of valence electrons in case of non-metals.
along a group and a period in modern periodic table.
F(9) has electronic configuration of 2, 7. It is a non-
Ans : [CBSE 2013, 2012] metal. Its valency is equal to 1.
Atomic size increases down the group and decreases
along a period from left to right in the periodic table. 54. An element X belongs to 3rd period and group 17 of the
Metallic character increases down the group and it periodic table. State its (a) electronic configuration,
decreases along a period from left to right. (b) valency. Justify your answer with a reason.
Ans : [CBSE2012]
48. Elements in Periodic table show periodicity in
a. 2, 8, 7; because it has 3 shells as it belongs to
properties. List any four such properties.
3rd period. Group 17 means 7 valence electrons.
Ans : [CBSE2013] b. Valency = 1
Valence electrons, Valency, Atomic size, Metallic It can gain 1 electron to become stable i.e. to
character. complete its octet.
55. Choose from the following: are 2, 8, 3 and 2, 8, 7 respectively. Find the atomic
20
Ca, 3Li, 11Na, 10Ne number of these elements. State the nature and
formula of the compound formed by union of these
a. An element having two shells completely filled elements.
with electrons.
Ans : [CBSE 2012]
b. Two elements belonging to same group of the
periodic table. A has 2 + 8 + 3 = 13 as its atomic number B has 2 +
Ans : [CBSE 2012] 8 + 7 = 17 as its atomic number
a. 10
Ne (2, 8)
b. 3
Li(2, 1) and 11
Na(2, 9, 1) belong to the same
group.
AB3 is the formula of compound. It is an ionic
56. Why do all elements of the
compound.
a. same group have similar properties?
b. same period have different properties? 61. The atomic number of three elements are given below:
Ans : [CBSE 2012]
Element (symbol) A B C
a. It is due to same number of valence electrons
which will decide the chemical properties. Atomic number 5 7 10
b. They differ in number of valence electrons, Write the symbol of element which belongs to (a)
therefore they differ in chemical properties. They group 13, (b) group 15 of the periodic table. State
have the same number of shells. the period to which these elements belongs to. Give
reason for your answer.
57. An element ‘E’ has the following electronic
configuration: Ans : [CBSE 2012]
a. A(2, 3) belongs to group 13 because it has 3
K L M valence electrons.
2 8 6 b. B(2, 5) belongs to group 15 because it has 5
valence electrons. It belongs to 2nd period because
a. To which group of the periodic table does element
it has 2 shells.
E belong to?
b. To which period of the periodic table does element
E belong to?
c. State the number of valence electrons present in
element E.
d. State the valency of the element E.
Ans : [CBSE 2012]
a. E (2, 8, 6) belongs to group 16,
b. It belongs to 3rd period.
c. It has 6 valence electrons.
d. The valency of E is 2.

58. Choose from the following: 4Be, 9F,

19
K, 20Ca
a. The element having one electron in the outermost
shell.
b. Two elements of the same group. 62. The electronic configuration of two elements A and B
Ans : [CBSE 2012] are 2, 8, 7 and 2, 8, 8, 2 respectively. Write the atomic
a. K(2,8,8,1) has one valence electron, number of these elements. What will be formula of the
19
compound formed and the nature of bond between
b. 4
Be(2, 2) and 20Ca(2, 8, 8, 2) belongs to the same them when these two elements chemically combine
group. together?
59. An element has atomic number 13.
Ans : [CBSE 2012]
a. What is the group and period number to which A - 2 + 8 + 7 = 17 is its atomic number.
this element belongs to? B - 2 + 8 + 8 + 2 = 20 is its atomic number.
b. Is the element a metal or a non-metal? Justify A(2, 8, 7) B(2, 8, 8, 2)
your answer.
Ans : [CBSE 2012]
a. It belongs to group 13, 3rd period because it has
3 valence electrons and 3 shells.
b. It is a metal because it can lose 3 electrons to The nature of bond is ionic bond.
become stable.

60. The electronic configuration of two elements A and B

63. The atomic number of these elements are given below: and why?
Ans : [CBSE 2011]
Element (symbol) A B C
Metallic character of elements decreases along a
Atomic number 3 6 9 period from left to right because atomic size decreases,
Write the symbol of element which belongs to tendency to lose electrons decreases.
a. group 1,
b. group 14 of the periodic table. 69. How does valency of the elements vary
State the period of the periodic table to which these a. in going down a group, and
elements belong to. State reason to support your b. in going from left to right in a period of the
answer. periodic table?
Ans : [CBSE 2012] Ans : [CBSE 2011]

c. A(3) has electronic configuration 2, 1. It belongs a. It remains the same.

to group 1. Hence the number of valence electrons b. It first increases till middle, then decreases.
is 1.
70. In the periodic table, how does the tendency of atoms
d. B(6) has electronic configuration 2, 4. It belongs
to lose electrons change on going from
to group 14, valence electrons = 4.
a. left to right across a period?
They belong to second period because they have
b. top to bottom in a group?
2 shells.
Ans : [CBSE 2011]
64. How the electronic configuration of the atom of a. Tendency to lose electron(s) decreases across the
an element is related to its position in the modern period from left to right.
periodic table? Explain with one example. b. Tendency to lose electron(s) increases down in a
Ans : [CBSE 2011] group.
Period No. = Number of shells
71. Give reasons:
Group No. = Number of valence electrons or valence
a. Elements in a group have similar chemical
electrons +10.
properties.
Example
b. Elements of Group 1 form ions with a charge of
Na(11): 2, 8,1. It has 1 valence electron, it belongs to
+1.
group 1. Also Al (13): 2, 8, 3. It has 3 shells, therefore
it belongs to 3rd period. Ans : [CBSE 2011]
a. It is due to the same number of valence electrons.
65. The atomic number of three elements, X, Y and Z are b. Group-1 elements can lose one electron to form
9, 11 and 17 respectively. Which two of these elements positive ions with charge equal to +1.
will show similar chemical properties? Why?
Ans : [CBSE 2011] 72. What is meant by periodicity of properties of
elements? Why are the properties of elements placed
X(9) : 2, 7
on the same group of the periodic table similar?
Y(11) : 2, 8, 1
Z(17) : 2, 8, 7 Ans : [CBSE 2011]
X and Z have similar chemical properties because they The repetition of similar properties after a definite
have the same number of valence electrons. interval is called periodicity of properties. It is due to
the same number of valence electrons.
66. On the basis of electronic configuration, how will you
identify the first and the last element of a period? 73. Elements Mg and O respectively belong to group
Ans : [CBSE 2011] 2 and group 16 of the modem periodic table. If the
atomic number of Mg and O are 12 and 8 respectively,
1st element will have 1 valence electron whereas last
draw their electronic structures and show the process
element will have 8 valence electrons except in first
of formation of the compound by transfer of electrons
period in which last element has 2 electrons.
between them.
67. In the modern periodic table, the element Calcium Ans : [CBSE 2010]
(atomic number = 20) is surrounded by elements Mg(12): 2,8,2
with atomic numbers 12, 19, 21 and 38. Which of O(8): 2,6
these elements has physical and chemical properties
resembling those of Calcium and why?
Ans : [CBSE 2011]
Ca(20): 2, 8, 8, 2
Mg(12): 2,8, 2
Sr(38): 2, 8, 18, 8, 2
Mg and Sr has similar properties to Ca because each
of them have 2 valence electrons.

68. How does metallic character of the elements change

along a period in the periodic table from left to right
 Mg $ Mg2+ + 2e- b. A<D<B<C is the decreasing order of atomic size.
2, 8, 2 2, 8 c. B2O is the formula of oxide.
-
O + 2e $ O 2- d. D is a metalloid.
2, 6 2, 8
78. Give reasons for the following:
a. Lithium atom is smaller than sodium atom.
b. Chlorine (Atomic number 17) is more
electronegative than Sulphur (Atomic number 16)
74. State Mendeleev’s periodic law. Write two achievements Ans : [CBSE 2011]
of Mendeleev’s periodic table.
a. Li(3): 2, 1; Na(11): (2, 8, 1).
Ans : [CBSE 2009] Li has two shells, therefore it is smaller than Na
Properties of elements are a periodic function of their which has 3 shells.
atomic mass. b. Chlorine (17) is smaller than sulphur (16),
Achievements: therefore it is more electronegative than sulphur.
a. It could arrange all the elements discovered at
79. a. State the main characteristic of elements on which
that time.
b. It left some gaps for the elements to be discovered modern periodic table is based.
and helped in their discovery by predicting their b. No fixed position is assigned to hydrogen in the
properties. periodic table, why?
Ans : [CBSE 2012]
75. The elements of the second period of the periodic
a. Modem periodic table is based on the trend of
table are given below:
increasing order of atomic number. Elements
Li, Be, B, C, N, O, F
of same group have same number of valence
a. Give reason to explain why atomic radii decreases
electrons.
from Li to F.
b. Hydrogen resembles with both group 1 and group
b. Identify the most (i) metallic and (ii) non-metallic
17 elements, therefore it does not have a fixed
element.
position.
Ans : [CBSE 2008(C)]
a. It is because effective nuclear increases due to
increase in forces of attraction between more
electrons with more protons, even though number
of shells remain the same.
b. (i) Li is the most metallic element, (ii) F is the
most non-metallic element.

76. The elements of the third period of the Periodic Table

are given below:

Group I II III IV V VI VIII

Period 3 Na Mg Ai Su P S Cl
a. Which atom is bigger, Na or Mg? Why?
b. Identify the most (i) metallic and (ii) non-metallic
element in Period 3. 80. Two elements M and N belong to group 1 and 2
respectively and are in the same period of the periodic
Ans : [CBSE 2008(C)]
table. How do the following properties of M and N
a. Na is bigger because it has 11p and 11e i.e., less vary?
forces of attraction than in Mg which has 12 a. Sizes of their atoms.
protons and 12 electrons and has more forces of b. Their metallic character.
attraction, due to more effective nuclear charge. c. Their valencies in forming oxides.
b. (i) Na is the most metallic element, (ii) Cl is the d. Formulae of their chlorides.
most non-metallic element. Ans : [CBSE 2012, 2009]
77. Given below are four elements with their atomic a. M has bigger size than N.
numbers: b. M has more metallic character than N.
A(16), B(11), C(3), D(14) c. M has valency equal to 1, N has valency equal
a. Identify the elements which belong to the same to 2.
group of the Modem periodic table. d. MCl and MCl2 are formula of their chlorides.
b. Arrange the elements in decreasing order of the
atomic size. 81. The following table shows the elements represented by
c. Write the formula of oxide of B. the letters A, B, C, D, E, F, G and H.
d. Which of these elements is a metalloid?
Group 1 2 13 14 15 16 17 18
Ans : [CBSE 2011]
Element A B C D E F G H
a. C(3) and B( 11) belongs to the same group.
 a. Which of the elements has the atomic size (i) They will be placed in the same slot because they
biggest and (ii) smallest? have similar chemical properties due to same number
b. Which element has valency equal to (i) 3 and (ii) of valence electrons.
zero?
87. The electronic configuration of an element X is 2, 8,
Ans : [CBSE2012]
8, 2. To which period and group of periodic table does
a. (i) A has the biggest size. (ii) G has the smallest the element X belong to? State the valency and justify
size. your answer in each case.
b. (i) C has valency equal to 3. (ii) H has valency Ans : [CBSE 2012]
equal to zero.
It belongs to 4th period because it has four shells.
82. a. State Modern Periodic Law It belongs to group 2 because it has 2 valence
b. Elements A, B, C and D have atomic number 1, electrons. X has a valency equal to 2 because it can
8, 11, 19 respectively. Choose the odd element and lose 2 electrons to become stable.
give reason for your answer.
88.
Ans : [CBSE 2012]
a. Modern Periodic Law: It states ‘properties of 89. The atomic number of three elements are given below:
elements are a periodic function of their atomic A(5), B(7), C(10)
number’. Write the symbol of element which belongs to (a)
b. B(8): 2, 6 is an odd element because it has 6 group 13, (b) group 15 of the periodic table. State
valence electrons whereas others have 1 valence the period of periodic table to which these elements
electron. belong to. Give reason to your answer.
Ans : [CBSE 2012]
83. Arrange the following elements in descending order
of their atomic size and give reason for your answer. a. A(5): 2, 3 belong to group 13 because it has 3
Mg(12), P(15), Cl(17), Ar(18) valence electrons.
b. B(7): 2, 5 belong to group 15 because it has 5
Ans : [CBSE 2012]
valence electrons.
Mg > P > Ar > Cl They i.e., A and B belong to second period because
As we move from left to right, atomic size decreases they have 2 shells.
due to increase in effective nuclear charge. Ar is bigger
than Cl due repulsion between 8 valence electrons. 90. Arrange the following elements in increasing order of
their atomic radii:
84. Na, Mg, A1 are the elements having one, two and a. Li, Be, F, N
three valence electrons respectively. Which of these b. Cl, At, Br, I
elements (a) has longest atomic radius, (b) is least Ans : [CBSE 2012]
reactive? Justify your answer stating reason for each.
a. F < N < Be < Li
Ans : [CBSE 2012, 2015]
b. Cl < Br < I < At
a. Na has the largest atomic radius due to least
effective nuclear charge due to less forces of 91. Study the variation in atomic radii of first group
attraction between 11 protons and 11 electrons. elements given below and arrange them in an
b. A1 is the least reactive element due to small its increasing order:
size and least tendency to lose electrons. a. Name the element which have the smallest and
the largest atoms
85. The atomic number of these elements are given below:
Group Na Li Rb Cs K
Element B O N C
Radius in pm 161 152 244 262 231
Atomic radius (in pm) 86 66 74 97
b. How does the atomic size vary as you go down
Arrange this elements in increasing order of their the group?
atomic numbers. Give reason for your answer. Ans : [CBSE 2011]
Ans : [CBSE 2012]
Li < Na < K < Rb < Cs
B(5), C(6), N(7), 0(8) is the increasing order of their a. Li is the smallest, Cs is the largest atom.
atomic numbers. b. Atomic size increases down the group.
It is because when we move along a period,
92. Atomic radii of the elements of second period are
atomic radii decreases due to increase in effective
given below:
nuclear charge due to increase in number of protons
and electrons continuously. Period II B Be O N Li C
86. Would you place the two isotopes Cl-35 and Cl-37 in elements
different slots because of their different atomic masses Atomic radius 88 111 66 74 152 77
or in the same slot because their chemical properties (in pm)
are same? Justify your answer.
a. Arrange them in decreasing order of their atomic
Ans : [CBSE 2012,2015] size.
 b. Are the elements now arranged in the pattern of a 96. Differentiate between the arrangement of elements
period in periodic table? in Mendeleev’s periodic table and Modern Periodic
c. Which elements have the largest and the smallest Table.
atoms? Ans : [CBSE Sample Paper 2017-2018]
d. How does the atomic radius change as you go
from left to right in a period. Mandeleev’s Periodic Modern Periodic Table
Ans : [CBSE 2011] Table
a. Li > Be > B > C > N > O It is based on increasing It is based on increasing
b. Yes, They belong to the second period. order of atomic mass. order of atomic number.
c. Li is the largest, oxygen is the smallest.
d. Atomic size decreases along a period from left to It has 8 groups and 6 It has 18 groups and 7
right. periods. periods.
Increasing order of Increasing order of
93. Li, Be, B, C are the elements of same period of Modem atomic mass could not atomic number can be
Periodic table. be maintained. maintained.
a. Arrange them in increasing order of their atomic
size.
97. Write the names given to the vertical columns and
b. In which shell (number) would last electron enter
horizontal rows in the Modern Periodic Table. How
for all of them.
does the metallic character of elements vary on
c. Calculate the valence electrons in each.
moving down a vertical column? How does the size of
d. Which element amongst them is most
atomic radius vary on moving from left to right in a
electropositive?
horizontal row? Give reason in support of your answer
Ans : [CBSE 2016] in the above two cases.
a. C < B < Be < Li Ans : [CBSE 2017]
b. Second shell
Vertical columns are called groups. Horizontal rows
c.
are called periods. Metallic character of elements
increases down the group because tendency to lose
electrons increases down the group due to increase in
atomic size. Atomic size goes on decreasing along the
period due to increase in effective nuclear charge due
They have 1, 2, 3, 4 valence electrons respectively. to increase in number of protons and electrons.
d. Li is the most electropositive element.

THREE MARKS QUESTIONS

94. An element X belongs to 3rd period and group 16 of

the Modern Periodic table.
a. Determine the number of valence electrons and
the valency of X.
b. Molecular formula of the compound of X when it
reacts with hydrogen and write its electron dot
diagram.
c. Name the element X and state whether it is
metallic or non-metallic.
Ans : [CBSE 2015] 98. An element ‘P’ (atomic number 20) reacts with an
a. X has 6 valence electrons and its valency is equal element ‘Q’ (atomic number 17) to form a compound.
to 2. Answer the following questions giving reason:
Write the position of ‘P’ and ‘Q’ in the Modem
b. H2X is its formula, Periodic Table and the molecular formula of the
compound formed when ‘P* reacts with ‘Q’.
c. X is sulphur. It is a non-metallic element. Ans : [CBSE 2017]
95. Two elements X and Y have atomic number 11 and P(20): 2, 9, 9, 2; Q(17): 2, 8, 7
16 respectively. ‘P’ belongs to group 2 and 4th period.
a. Write the electronic configuration of both. ‘Q’ belongs to group 17 and 3rd period.
b. Write the formula of the compound formed by
their combination (in terms of X and Y).
Ans : [CBSE 2014]
a. X(11): 2, 8, 1; Y(16): 2, 8, 6
b. X2Y is the formula of compound formed. PQ2 is the molecular formula of the compound formed.
99. Write the electronic configuration of two elements a. Metallic character decreases from left to right
X’ and ‘Y’ whose atomic numbers are 20 and 17 because atomic size decreases, tendency to lose
respectively. Write the molecular formula of the electrons decreases,
compound formed when element X’ reacts with b. Metallic character increases from top to bottom
element ‘Y’. Draw electron-dot structure of the in a group because atomic size increases due to
product and also state the nature of the bond formed which effective nuclear charge decreases.
between both the elements.
103. a.Identify the elements among the following which
Ans : [CBSE 2017, 2013]
will belong to the same group: H, He, Li, B, C.
X(20): 2, 8, 8, 2; Y(17): 2, 8, 7 b. State the group number of the recognised elements.
c. Name another one element belonging to the same
group.
Ans : [CBSE 2017]
a. H and Li belong to the same group.
X $ X 2 + 2 e- b. They belong to group 1.
Y + e- $ Y- c. Na (sodium) also belong to this group.

104. Justify the following with suitable reasons:

a. Cations are smaller than the corresponding atoms.
This bond is ionic bond. b. Size of atom increases as we move down the group.
c. Atomic size decreases as we move across a period.
100. What is periodicity in properties of elements with Ans : [CBSE 2017, 2014]
reference to the Modern Periodic Table? Why do all
the elements of the same group have similar properties? a. Cations are formed by loss of electrons, therefore
How does the tendency of elements to gain electrons effective nuclear charge increases, size of atom
change as we move from left in a period? State the decreases.
reason of this change. b. It is because number of shells goes on increasing
down the group.
Ans : [CBSE 2017]
c. It is because effective nuclear charge increases
The repetition of similar properties after a definite along a period.
interval is called periodicity of properties.
Tendency to gain electrons increases along a period 105. Name the element with atomic number 19.
from left to right because atomic size decreases. a. In which group it is placed?
b. To which period does it belong to?
101. The atomic number of an element is 19. c. Write its electronic configuration.
a. Write the electronic configuration of this element Ans : [CBSE 2017]
and determine (i) the valency of this element,
and (ii) whether this element is a metal or a non- The name of element is Potassium, K(19): 2, 8, 8, 1.
metal? a. It belongs to group 1.
b. Write the formula of the oxide of this element. b. It belongs to 4th period.
c. Is this element more reactive or less reactive than c. Its electronic configuration is 2,8 8,1.
Na (atomic number 11)? Justify your answer,
106. The atomic number of an element is 20.
giving example.
a. Write its electronic configuration and determine
Ans : [CBSE 2017] its valency.
a. 2, 8, 8, 1 b. Is it a metal or a non-metal?
i. Valency = 1 c. Write formula of its chloride.
ii. It is a metal. d. Is it more or less reactive than Mg(12)? Give
a. X2O reasons for your answer.
b. It is more reactive than Na(11) because it is large Ans : [CBSE 2017]
in size and it can lose electrons easily due to less
a. Ca(20): 2, 8 8, 2. Its valency is equal to 2.
effective nuclear charge.
b. It is a metal.
K reacts more vigorously with H2O than Na.
c. CaCl2.
102. Why is atomic number considered to be a more d. It is more reactive than Mg due to larger atomic
appropriate parameter than atomic mass for the size. It can lose electrons easily due to less effective
classification of elements in a periodic table? How nuclear charge.
does the metallic character of elements vary as we
107. The atomic number of an element is 12.
move (a) from left to right in a period, and (b) top to
a. Write its electronic configuration and determine
bottom in a group of the modem periodic table? Give
its valency.
reasons to justify your answer.
b. Is it more reactive or less reactive than Ca(20)?
Ans : [CBSE 2017] c. Is it a metal or a non-metal?
It is because chemical properties depend upon the d. Write the formula of its oxide.
number of valence electrons which is determined with Ans : [CBSE 2017]
the help of atomic number.
 a. Mg(12): 2, 8, 2. Its valency is equal to 2. b. It belongs to group 2 and 4th period.
b. It is less reactive than Ca. c. CaO + H2O $ Ca(OH)2
c. It is a metal.
d. MgO 112. An element X belongs to 3rd period and group 16 of
the Modern Periodic Table.
108. Out of the elements H(1), Be(4), Na(11) and Mg(12). a. Determine the number of valence electrons and
a. Write the pair of elements having similar chemical the valency of X.
properties. b. Molecular formula of the compound when X
b. State the group number of each pair, reacts with hydrogen and write its electron dot
c. Name one another element belonging to each of structure.
these groups. c. Name the element X and state whether it is
Ans : [CBSE 2017,2016] metallic or non-metallic.
a. Be(4) and Mg(12) have similar chemical properties. Ans : [CBSE 2016]
H( 1) and Na(ll) have similar chemical properties. a. X is sulphur, S(16): 2, 8, 6. It has 6 valence
b. Be and Mg belong to group 2, H and Na belong electrons. Its valency is equal to 2.
to group 1.
c. K belongs to group 1 and Ca belongs to group 2. b. H2X,

109. Calcium is an element with atomic number 20. Stating

the reason, answer each of the following questions: c. X is a non-metal.
a. Is calcium a metal or a non-metal?
b. Will its atomic radius be larger or smaller than
that of potassium with atomic number 19?
c. Write the formula of its oxide.
Ans : [CBSE 2016]
a. Calcium is a metal because it can lose electrons
to form cations.
b. Its atomic radius will be smaller due to more
number of protons and electrons, more forces of
attraction.
c. CaO

110. An element M with electronic configuration (2,8,2)

combines separately with ^NO 3h-, ^SO 4h2- and ^PO 4h
3-

radicals. Write the formula of the three compounds

so formed. To which group and period of the Modern 113. How does tendency to lose electrons change in the
Periodic Table does the element M belong to? Will Modern Periodic Table in (a) a group, (b) a period
M form covalent or ionic compounds? Give reason to and why?
justify your answer. Ans : [CBSE 2016]
Ans : [CBSE 2016] a. In a group, tendency to lose electrons increases
M(2, 8, 2). It has valency equal to 2. down the group because atomic size increases,
forces of attraction between the valence electron
and nucleus decreases.
b. In a period, tendency to lose electrons decreases
due to decrease in atomic size due to more effective
nuclear charge.
M belongs to group 2.
It belongs to 3rd period. 114. Three elements ‘X’, ‘Y’ and ‘Z’ have atomic numbers
M will form ionic compound because M can easily lose 7, 8 and 9 respectively.
electrons. a. State their positions (Group number and period
Bond will be formed by transfer of electrons. number both) in the Modern Periodic Table.
b. Arrange these elements in decreasing order of
111. An element X’(Atomic number 20) burns in the their atomic radii.
presence of oxygen to form a basic oxide. c. Write the formula of the compound formed when
a. Identify the element and write its electronic X’ combines with ‘Z’.
configuration. Ans : [CBSE 2016]
b. State its group number and period number in the
Modern Periodic Table. X(7): 2, 5,
c. Write a balanced chemical equation for the Y(8): 2, 6
reaction when this oxide is dissolved in water. Z(9): 2, 7
a. X belong to Group 15 and 2nd period.
Ans : [CBSE 2016]
Y belong to Group 16 and 2nd period.
a. X is calcium because it forms CaO (basic oxide). Z belong to Group 17 and 2nd period.
Its electronic configuration is 2, 8 8, 2. b. X > Y > Z
 characteristics in tabular form:
a. The number of electrons in their atoms.
c. b. The size of their atoms.
c. Their metallic character.
d. Their tendency to lose electrons.
115. The atomic number of Na and Mg are 11 and 12 e. The formula of their oxides.
respectively and they belong to the same period f. The formula of their chlorides.
a. Which one should have smaller atomic size?
Ans : [CBSE 2015, 2014]
b. Which would be more electropositive?
c. To which group would each one belong? a. P has 1 valence electron, Q has 2 valence electrons.
Ans : [CBSE 2016] b. P is bigger than Q.
c. P is more metallic than Q.
Na(11): 2, 8, 1; Mg(12): 2, 8, 2 d. P can lose electrons more easily than Q.
a. Mg will have smaller size. e. P2O and QO
b. Na is more electropositive. f. PCl and QCl2
c. Na(11) belongs to group 1 whereas Mg(12)
belongs to group 2. 121. Taking example of an element of atomic number 16,
explain how the electronic configuration of the atom
116. Explain the basic character of oxides of elements down of an element relates to its position in the Modern
the group and across the period. Periodic Table and how valency of an element is
Ans : [CBSE 2016] calculated on the basis of its atomic number?
Basic character of oxides increases down the group Ans : [CBSE 2015]
because metallic character increases. S(16) has electronic configuration of 2,8, 6,
Basic character of oxides decreases along the Group number = valence electrons + 10
period from left to right because non¬metallic = 6 + 10 = 16
character increases, metallic character decreases. Period number = Number of shells = 3 Valency
= 8 - valence electrons =8-6=2
117. Describe the basic character of oxides of third period
elements across the period from left to right. 122. The atomic number of an element X’is 20.
Ans : [CBSE 2016] a. Determine the position of the element “X’ in the
periodic table.
Na2O, MgO are basic oxides.
b. Write the formula of the compound formed when
SiO2, Al2O3 are amphoteric oxides.
‘X’ reacts/combines with another element *Y’
P2O5, SO2, Cl2O7 are acidic oxides.
(atomic number 8).
Basic character of oxides decreases across the period.
c. What would be the nature (acidic or basic) of the
118. Write the number of periods in the modern periodic compound formed? Justify your answer.
table. State the changes in valency and metallic Ans : [CBSE 2015]
character of elements as we move from left to right in X(20): 2, 8, 8, 2; Y(8): 2, 6
a period. Also state the changes, if any, in the valency a. It belongs to group 2, 4th period because its
and atomic size of elements as we move down the valence electrons are 2 and no. of shells = 4
group.
Ans : [CBSE 2015, 2013] b.
There are 7 periods in Modern Periodic Table.
Valency first increases and then decreases. Metallic
c. Compound formed will be basic because “X’ is a
character decreases along a period from left to right.
metal.
There is no change in valency down the group.
Atomic size increases down the group. 123. An element X’ is placed in 13th group and 3rd period
of Modern Periodic Table. Answer the following
119. How many groups and periods are there in the Modern
stating reason for your answer.
Periodic Table? How do the atomic size and metallic
a. Write the electronic configuration of the element
character of elements vary as we move
X’.
a. down a group and
b. Write the formula of the compound formed when
b. from left to right in a period?
element X’ reacts with another element ‘Y’,
Ans : [CBSE 2015] having atomic number 17.
There are 7 periods in Modern Periodic Table. c. Will oxide of this element be acidic or basic?
Valency first increases and then decreases. Metallic Ans : [CBSE 2015]
character decreases along a period from left to right.
X is Aluminium (13); Y(17) 2, 8, 7
There is no change in valency down the group.
a. 2, 8, 3
Atomic size increases down the group.

120. Two elements P and Q belong to the same period

b.
of the modern periodic table and are in Group-1
and Group-2 respectively. Compare their following
 c. It will be amphoteric i.e., it is acidic as well as questions:
basic. a. Name the element which forms only covalent
compounds.
124. Given below are some elements of the Modern Periodic b. Name the element which is a metal with valency
Table. Atomic number of the element is given in the of three.
parentheses: c. Name the element which is a non-metal with
A(4), B(9), C(14), D(19), E(20) valency of three.
a. Select the element that has only one electron d. Out of B and C, whose atomic radius is bigger
in the outermost shell. Also write the electronic and why?
configuration of this element. e. Write the common name of the family to which
b. Which two elements amongst these belong to the the elements D and F belongs to?
same group? Give reason for your answer.
Ans : [CBSE 2015]
c. Which two elements amongst these belong to the
same period? Which among the two has bigger a. E is an element which form covalent compounds.
atomic radius? b. B is a metal with a valency of 3.
Ans : [CBSE 2015] c. C is a non-metal with a valency of 3.
d. B has bigger size.
a. D(19): 2,8,8,1 has 1 valence electron. e. D and F belong to Noble gases.
b. A(4): 2, 2 and E(20): 2, 8, 8, 2 belong to same
group because they have the same number of
valence electrons.
c. A(2, 2), B(2, 7) belong to the same period. A has
bigger atomic radius than B.

125. Write the main aim of classifying elements. Name

the basic property of elements which is used in the
development of Modern Periodic Table. State the
Modern Periodic Law. On which side (part) of the
Modern Periodic Table do you find metals, metalloids
and non- metals?
Ans : [CBSE 2015]
Classification is done so as to study the properties of
118 elements easily. Modern periodic table is based on
atomic number of the atom an element. ‘Properties 128. Four elements P, Q, R and S belong to third period of
of elements are a periodic function of their atomic the Modern Periodic Table and have respectively 1, 3,
numbers.’ Metals are placed on the left and middle, 5 and 7 electrons in their outermost shell. Write the
non-metals are placed on the right and Metalloids are electronic configurations of Q and R and determine
placed on the border line between metals and non- their valencies. Write the molecular formula of the
metals in a zig-zag manner. compound formed when P and S combine.
Ans : [CBSE 2015]
126. The elements 4Be, 12
Mg and 20Ca having two valence
electrons in their valence shells are in periods 2, 3 and P: 2, 8, 1 Valency = 1
4 respectively of the modern periodic table. Answer Q: 2, 8, 3 Valency = 3
the following questions associated with these elements, R: 2, 8, 5 Valency = 3
giving reason in each case: S: 2, 8, 7 Valency = 1
a. In which group should they be placed?
b. Which one of them is least reactive?
c. Which one of them has the largest atomic size?
Ans : [CBSE 2015, 2014]
PS is the formula of compound.
a. They belong to group 2.
b. Be is least reactive. 129. Study the following table in which positions of six
c. Ca has largest atomic size. elements A, B, C, D, E and F are shown as they are
in the modern periodic table:
127. In the following table, the position of six elements A,
B, C, D, E and F are given as they are in the Modern Group " 1 2 3-12 13 14 15 16 17 18
Periodic Table:
.Period
Group " 1 2 3-12 13 14 15 16 17 18
2 A B C
.Period
3 D E F
2 A C D On the basis of the above table, answer the following
3 B E F questions:
a. Name the element which forms only covalent
On the basis of the above table, answer the following
compounds.
 b. Which element is a metal with a valency of one? along a period.
c. Which element is a non-metal with a valency of
two? 133. What is meant by ‘group’ in the modern periodic
d. Out of D and E, which has a bigger atomic radius table? How do the following change on moving from
and why? top to bottom in a group?
e. Write the formula of the compound formed when a. Number of valence electrons.
B combines with D. b. Number of occupied shells.
c. Size of atoms.
Ans : [CBSE 2014]
d. Metallic character of elements.
a. E forms only covalent compounds. e. Effective nuclear charge experienced by valence
b. D is a metal with valency of 1. electrons.
c. B is a non-metal with valency of 2. Ans : [CBSE 2014]
d. D has bigger atomic size because it has less
effective nuclear charge. The vertical column of the periodic table is called
group.
e. a. Number of valence electrons remains the same in
a group.
b. Number of occupied shells goes on increasing
DB2 is formula of the compound. down a group.
c. Size of atom increases down the group.
130. The electrons in the atoms of four elements A, B, C d. Metallic character of element increases down the
and D are distributed in three shells havingl, 3, 5 and group.
7 electrons in the outermost shell respectively. State e. Effective nuclear charge decreases down the group.
the period in which these elements can be placed
in the modern periodic table. Write the electronic 134. The electronic configuration of 4 elements A, B, C and
configuration of the atoms of A and D and the D are given as under:
molecular formula of the compound formed when A A-2, 1; B-2, 2; C-2, 8, 2; D-2
and D combine. a. Which amongst them belongs to the same group?
Ans : [CBSE 2014] Name it.
b. Which amongst them belong to the same period?
A: 2, 8, 1 Name it.
B: 2, 8, 3 c. Which amongst them is an inert element? Name
C: 2, 8, 5 it.
D: 2, 8, 7
Ans : [CBSE 2014]
They belong to the 3rd period.
a. B and C belong to the same group, 2nd group;
Be and Mg.
b. A and B belong to the same period, 2nd period;
Li and Be.
AD is the molecular formula. c. D is the inert; It is Helium (He).

131. Based on the group valency of elements state the 135. Two elements X and Y have atomic 12 and 17
formula for the following giving justification for each: respectively.
a. Oxides of 1st group elements, a. Write the electronic configuration of both these
b. Halides of the elements of group 13, and elements.
c. Compounds formed when an element of group 2 b. Which type of bond will they form?
combines with an element of group 16. c. Write the formula of the compound formed by
their combination (in terms of X and Y).
Ans : [CBSE 2014]
Ans : [CBSE 2014]
a. M2O
b. MCl3 a. X: 2, 8, 2; Y: 2, 8,7
c. CaO b. They will form ionic bond.

132. a.Define the following terms (i) Valency, (ii) Atomic

c.
size
b. How do the valency and the atomic size of the
elements vary while going from left to right along XY2 is the formula of the compound.
a period in the modern periodic table?
Ans : [CBSE 2014] 136. An element X (atomic number 17) reacts with an
element Y (atomic number 20) to form a compound.
a. (i) Valency: It is the number of electrons lost or a. Write the position of these elements in the modern
gained or shared by an atom. periodic table.
(ii) Atomic size: It is the distance between centre b. Write the formula of the compound formed.
of the nucleus and outermost shell of an atom. Justify your answer in each case.
b. Valency first increases till middle and then
Ans : [CBSE 2013]
decreases. Atomic size decreases from left to right
a. X: 2, 8, 7 belongs to 3rd period, group 17, because
 it has 3 shells and 7 valence electrons. 2, 8, 7 is the electronic configuration.
Y: 2, 8, 8, 2 belongs 4th period, group 2, because a. Its valency is equal to 1 because it can gain 1
it has 4 shells and 2 valence electrons. electron to become stable.
b. YX2, is the formula of the compound, because Y b. Non-metals because it can gain an electron to
has valency 2, X has valency 1. form anion.
c. It is bigger in size than F (1st element) but smaller
137. Given below are some elements of the modern periodic than all other members because it has 3 shells, F
table: has 2 shells, others have more than 3 shells.
4
Be, 9F, 14Si, 19K, 20Ca
141. F, Cl and Br are the elements each having seven
a. Select the element that has one electron in valence electrons. Which of these (a) has the largest
the outermost shell and write its electronic atomic radius, (b) is most reactive? Justify your
configuration. answer stating reason for each.
b. Select two elements that belong to the same Ans : [CBSE 2012]
group. Give reason for your answer.
a. Br has the largest atomic size because it has 4
c. Select two elements that belong to the same
shells.
period. Which one of these two has bigger atomic
b. F is the most reactive v it can give electrons most
size?
easily due to its smallest size.
Ans : [CBSE 2013]
a. K: 2, 8, 8, 1 142. Na/Mg and A1 are the elements having one, two and
19
three valence electrons respectively. Which of these
b. 4
Be, 20Ca belong to the same group because both elements (a) has the largest atomic radius, (b) is least
have same number of valence electrons. reactive? Justify you answer stating reason for each.
Be: 2, 2; Ca: 2, 8, 8, 2 Ans : [CBSE 2012]
c. 4
Be, 9F belong to the same period. 4Be has bigger
atomic size than 9F. Na has largest atomic radii due to 11 protons and 11
electrons and least effective nuclear charge. Na is most
138. The elements Li, Na and K each having one valence reactive because it can lose an electron easily due to
electron, are in period 2, 3 and 4 respectively of its large size and least effective nuclear charge.
modern periodic table.
a. In which group of the periodic table should they 143. a.How are the following related?
be placed? i. Number of valence electrons of different
b. Which one of them is least reactive? elements in the same group.
c. Which one of them has the largest atomic radius? ii. Number of shells of elements in the same
d. Give reason to justify your answer in each case. period.
b. How do the following change?
Ans : [CBSE 2013]
i. Number of shells of elements as we go down a
a. They belong to group 1 because they have one group.
only valence electron. ii. Number of valence electrons of elements on
b. Lithium (Li) is the least reactive because it moving from left to right in a period.
is smallest in size, has least tendency to lose iii. Atomic radius in moving from left to right
electrons. along a period.
c. K has largest atomic radius because it has iv. Atomic size as we go down a group.
maximum number of shells. Ans : [CBSE 2012]
139. Four elements P, Q, R and S have atomic numbers a. i. Same number of valence electrons.
12, 13, 14 and 15 respectively. Answer the following ii. Number of shells remains the same in a
questions giving reasons: period.
a. What is the valency of Q? b. i. Number of shells goes on increasing down the
b. Classify these elements as metals and non-metals. group.
c. Which of these elements will form the most basic ii. Number of valence electrons goes on increasing
oxide? in a period from left to right.
Ans : [CBSE 2013] iii. Atomic radius decreases along a period from
left to right.
a. Q(2, 8, 3) has valency = 3
iv. Atomic size increases down a group.
b. P, Q are metals, R and S are non¬metals.
c. P will form the most basic oxide. 144. a.How many periods are there in the Modem
Periodic Table of elements?
140. The atomic number an element is 17. Predict:
b. How do atomic radius, valency and metallic
a. its valency.
character vary down a group?
b. whether it is a metal or a non-metal?
c. How do atomic size and metallic character of
c. its relative size with respect to other members of
elements vary as we move from left to right in a
the group.
period?
Justify your answer in each case.
Ans : [CBSE 2012]
Ans : [CBSE 2013]
a. There are 7 periods.
 b. Atomic radius and Metallic character increases (ii) Electropositivity decreases across the period
down the group. Valency remains the same in a from left to right.
group. b. Atomic number increases across the period as well
c. Atomic size and metallic character decrease along as down the group.
a period from left to right in a period.
150. (a) Identify the element that have two completely
145. Explain the variation in the following properties of the filled shells and the number of valence electrons
elements in periodic table: in each case if atomic numbers are: (i) 1, (ii) 2,
a. Atomic radius in the periodic table, (iii) 7, (iv) 8
b. Metallic character in a period, (b) Analyse which amongst them is inert.
c. Valency in a group. Ans : [CBSE 2014]
Ans : [CBSE 2012] a. (i) 2, 8, 1: Sodium
a. Atomic radius and Metallic character increases (ii) 2, 8, 2: Magnesium
down the group. Valency remains the same in a (iii) 2, 8, 7: Chlorine
group. (iv) 2, 8, 8: Argon
b. Atomic size and metallic character decrease along (b) Argon is inert.
a period from left to right in a period.
151. The atomic number of K and Ca is 19 and 20
146. The elements of group 18 of the periodic table are respectively and they belong to same period.
given: a. Which amongst them would have smaller atomic
He, Ne, Ar, Kr, Xe, Rd, Dg size?
a. The elements of this group are unreactive, why? b. Which one would be more electro¬positive?
b. Which atom is bigger in size Ne or Ar and why? c. To which group would each one belong to?
Ans : [CBSE 2012] Ans : [CBSE 2014]
a. It is because they have their octet complete i.e., a. Ca has smaller atomic size.
stable electronic configuration. b. K is more electropositive.
b. Ar has bigger atomic size than Ne because Ar has c. K belongs to group 1, Ca belongs to group 2.
3 shells while Ne has 2 shells; Ar (2, 8, 8), Ne (2,
8) 152. The position of three elements A, B and C in the
periodic table are indicated below:
147. (a) State modern periodic law. Ans :
(b) How many groups and periods are present in the
modern periodic table? Group 16 Group 17
(c) State how the problem of placing (a) hydrogen, - - (First Period)
(b) isotopes of an element has been solved in this
periodic table. - A (Second Period)
Ans : [CBSE 2012] - - (Third Period)
a. Properties of elements are a periodic function of B C Fourth Period)
their atomic numbers’. a. State whether element C would be a metal or a
b. There are 18 groups and 7 periods. non-metal. Why?
c. (i) Hydrogen is placed along with group 1 as well b. Which is the more active element, A or C? Why?
as halogens because it resembles with both of c. Which type of ion (cation or anion) will be formed
them. by the element C? Why?
(ii) Isotopes do not need a separate place as they Ans : [CBSE 2011]
have the same atomic number.
a. O is a non-metal because it has 7 valence electrons.
148. a.Predict which of the following will form anions It can gain one electron to form an anion.
and which will form cations. b. A is more reactive than C because it is smaller in
(i) Na, (ii) Al, (iii) Cl, (iv) O size, therefore it can gain electron(s) easily.
b Name two elements that are inert.
153. Atoms of seven elements A, B, C, D, E, F and G have
Ans : [CBSE 2014]
a different number of electronic shells but have the
a. Cl and O will form anions i.e., Cl- and O2- same number of electrons in their outermost shells.
Na and A1 will form cations i.e., Na+ and Al3+. The elements A and C combines with chlorine to form
b. He and Ne are inert elements. an acid and common salt respectively. The oxide of
element A is liquid at room temperature and it is a
149. a.How does electropositivity of elements gets neutral substance, while the oxides of the remaining
affected as we move (i) down the group, (ii) across six elements are basic in nature. Based on the above
the period? information, answer the following question:
b. Which atomic property increases both ways: as a. What could the element A be?
we move across the period or down the group? b. Will elements A to G belong to the same period
Ans : [CBSE 2014] or same group of the periodic table?
a. (i) Electropositivity increases down the group. c. Write the formula of the compound formed by the
reaction of the element A with oxygen.
 d. Show the formation of the compound by the a. 2, 8, 2 is the electronic configuration of F.
combination of element C with chlorine with the b. No. of valence electrons = 2.
help of electronic structure. c. Three shells are present in F.
e. What would be the ratio of number of combining d. H > G > F > E is the decreasing order of atomic
atoms in a compound formed by the combination size.
of element A with carbon? e. F is a metal.
f. Which one of the given elements is likely to have f. B has biggest atomic size.
the smallest atomic radius?
156. a.Why did Mendeleev leave gaps in his periodic
Ans : [CBSE 2010]
table?
a. A is hydrogen. b. State any three limitations of Mendeleev’s periodic
b. A and G will belong to the same group. table.
c. H2O is the formula of the compound. c. How do the electronic configuration of atoms
d. C is sodium. change in a period with increase in atomic number.
Na $ Na+ + e- or C $ C+ + e- Ans : [CBSE 2009]
Cl + e- $ Cl- or Cl + e- $ Cl-
a. He left gaps for the new elements which are to be
discovered.
b. (i) Increasing order of atomic mass could not be
maintained.
e. CA4 i.e., 1:4 (ii) Position of hydrogen was not justified.
f. A has smallest atomic radius. (iii) Isotopes could not be placed in different
154. In the following table, six elements A, B, C, D, E
slots due to different atomic mass but same
and F (here letters are not the usual symbols of the properties.
elements) of the Modern Periodic Table with atomic c. Number of valence electrons keep on increasing
numbers 3 to 18 are given as follows: along a period from left to right in a period.

157. a.What is meant by periodicity in properties of

3 4 5 6 7 8 9 10
elements with reference to the periodic table?
A E G b. Why do all the elements of the same group have
11 12 13 14 15 16 17 18 similar properties?
c. How will the tendency to gain electrons change as
B C D F we go from left to right across a period. Why?
a. Which of these is (i) a noble gas, (ii) a halogen? Ans : [CBSE 2009]
b. If B combines with F, what would be the formula
a. The repetition of similar properties after regular
of the compound formed?
intervals is called periodicity in properties.
c. Write the electronic configurations of ‘C’and’E’.
b. It is because they have the same number of
Ans : [CBSE 2010] valence electrons.
a. (i) G is a noble gas, (ii) F is a halogen. c. Tendency to gain electrons increases from left to
b. BF is the formula of compound. right across the period due to decrease in atomic
c. C: 2, 8, 2 E: 2, 8, 6 size.

155. In the following table, are given eight elements A, 158. The position of three elements A, B and C in the
B, C, D, E, F, G and H (here letters are not the Periodic Table is shown below:
usual symbols of the elements) of the Modem Periodic
Table with the atomic numbers of the elements in Group 16 Group 17
parenthesis. - -
Period Group 1 Group 2 - A
2 A(3) E(4) - -
3 B(11) F(12) B C
4 C(19) G(20) Giving reasons, explain the following:
a. Element ‘A’ is a non-metal.
5 D(37) H(38) b. Element ‘B’ has a larger atomic size than element
a. What is the electronic configuration of‘F? ‘C’.
b. What is number of valence electrons in ‘F’ ? c. Element ‘C’ has a valency of 1.
c. What is number of shells in *F’ ? Ans : [CBSE 2008C]
d. Arrange E, F, G, H in decreasing order of atomic
a. A is a non-metal because it has 7 valence electrons,
size.
it can gain one electron to form anion.
e. State whether F is a metal or a non¬metal.
b. B has less electrons and protons, less forces of
f. Out of three elements B, E and F, which one has
attraction between the nucleus and valence
biggest atomic size.
electrons, therefore it is bigger in size.
Ans : [CBSE 2010] c. C can gain 1 electron to become stable, therefore
 its valency is equal to 1. group of the periodic table. Their atomic numbers are
4, 12, 20 respectively
159. The position of three elements A, B and C in the a. Write the electronic configuration of these
Periodic Table is shown below: elements.
b. Write the valency exhibited by them,
Group " 1 2 13 14 15 16 17
c. Which three elements will be the most reactive?
Period
. Ans : [CBSE 2013]
a.
1 B
2 A Shell K L M N

3 C Be(4) : 2 2

Giving reasons, explain the following: Mg(12) : 2 8 2

a. Element A is a non-metal. Ca(20): 2 8 8 2
b. Atoms of element C has a larger size than atoms
of element A. b. Valency is 2.
c. Element B has a valency of 1. c. Ca is the most reactive metal.
Ans : [CBSE 2009C]
a. A is a non-metal because it can gain one electrons
to form anion.
b. C has more number of shells i.e., it has 3 shells
because it belongs to 3rd period whereas A has 2
shells as it belongs to 2nd period.
c. B can lose 1 electron to become stable, therefore
its valency is equal to 1.

160. What physical and chemical properties of elements

were used by Mendeleev in creating his periodic
table? List two observations which posed a challenge
to Mendeleev’s Periodic Law.
Ans : [CBSE 2009]
a. Increasing order of atomic mass was the physical 163. In the figure given below the first 20 elements are
property. jumbled up. Carefully observe the figure and answer
b. Formulae of oxides and hydrides was the chemical the following questions:
property.
i. Increasing order of atomic mass could not be
maintained.
ii. Position of isotopes posed a challenge for the
classification of elements.

161. Table given below shows a part of the modern periodic

table.

H He
Li Be B C N O F Ne
a. Pick out the two elements which are known as
Na Mg Al Si P S Cl Ar alkali metals.
Using this table, explain why b. Pick out the two elements which have valency of
a. Li and Na are considered as active metals. 4.
b. Atomic size of Mg is less than that of Na. c. Pick out two elements which belong to group 16
c. Fluorine is more reactive than chlorine. of the periodic table.
Ans : [CBSE 2009] Ans : [CBSE 2013]

a. Li and Na have largest atomic size in respective a. Na, K are alkali metals.
period, therefore they can lose an electron easily, b. C, Si have valency equal to 4
hence they are active metals. c. O and S belongs to group 16.
b. Mg has 12 protons and 12 electrons which has
164. Examine elements of the third period: Na, Mg, Al, Si,
more forces of attraction, therefore, it is smaller
P, S, Cl and Ar Answer the following:
in size than Na which is having 11 protons and 11
a. Choose (i) Metals, (ii) Non-metals out of these
electrons.
elements.
c. F is smaller in size, it can gain electrons easily,
b. On which side of periodic table we find (i) metals
therefore, it is more reactive than Cl.
(ii) non-metals.
162. The element Be, Mg and Ca are placed in the second c. Name metalloids out of the elements given above.
 Where are they located in the periodic table? Ans : [CBSE 2015]
Ans : [CBSE 2011] a. Group 18
a. (i) Na, Mg, A1 are metals. b. They will form anions.
(ii) P, S, Cl, Ar are non-metals. c. F will have similar properties to ‘C’.
b. (i) Metals are placed on the left hand side and d. A has only one shell.
middle part of the periodic table. e. A and D both are inert elements.
(ii) Non-metals are placed on the right hand side f. C is the most abundant element in the Earth
of periodic table. crust.
c. Silicon is a metalloid. They are located between
metals and non-metals at the border line in a zig- FIVE MARKS QUESTIONS
zag manner.

165. As we move across a period in the periodic table, what

169. a.The modern periodic table has been evolved
is gradation in the following properties: (a) Atomic
through the early attempts of Dobereiner,
size, (b) Atomic number, (c) Electronegativity?
Newlands and Mendeleev. List one advantage and
Ans : [CBSE 2015] one limitation of all the three attempts.
a. Atomic size goes on decreasing across the period b. Name the scientists who first of all stated
from left to right. that atomic number of an element is a more
b. Atomic number goes on increasing along the fundamental than its atomic mass.
period from left to right. c. State modern periodic law.
c. Electronegativity goes on increasing along a Ans : [CBSE 2018]
period from left to right.
(a)
166. (a) Name metals among the first five elements of the Dobereiner Periodic Table
Modern Periodic Table. Advantage: It could predict the atomic mass of middle
(b) Write their symbols. elements quite correctly. Limitations: He could identify
(c) Write the formula of their oxides. only three triads of elements.
Newlands Periodic Table
Ans : [CBSE 2016, 2015]
Advantage: Every eight element had properties similar
a. Lithium and Beryllium are metals among first five to the first if elements are arranged in increasing order
elements. of atomic mass.
b. Lithium (Li), Beryllium (Be). Limitations: It was applicable only upto calcium only.
c. Li2O and BeO are the formulae of their oxides. No future elements could fit into it.
Mendeleev’s Periodic Table
167. Lithium, Sodium, Potassium are placed in the same
Advantage: He could classify all the elements
group on the basis of their similar properties. List discovered at that time into groups and periods.He
three such similar properties. also predicted the existence of new elements which
Ans : [CBSE 2015] were not discovered at time.
a. All of them are reactive metals. Limitations: No fixed position of hydrogen. Position of
b. They have 1 valence electron and form positive isotopes could not be sorted out.
ions with +1 charge. (b) Moseley:
c. They are largest in size in their respective periods. Properties of elements are a periodic function of their
atomic numbers.
168. The position of elements A, B, C, D, E, F and G in
the Modern Periodic Table is given as under: 170. Name the element which has
a. the electronic configuration 2, 8, 1.
Group " 16 17 18 b. a total of two shells, with 4 electrons in the
valence shell.
Period c. a total of three shells, with 3 electrons in the
. valence shell.
1 A d. one shell which is completely filled with electrons.
e. twice as many electrons in the second shell as in
2 B C D the first shell.
3 E F G Ans : [CBSE 2016]
a. In which group are inert elements placed? a. Sodium (2, 8, - 1)
b. What type of ions would ‘B’, ‘C’, ‘E’ and ‘F’will b. Carbon (2, 4)
form? c. Aluminium (2, 8, 3) i
c. Which element would have chemical properties d. Helium (2)
similar to ‘C’ ? e. Carbon (2, 4)
d. How many shells do ‘A’ have?
e. What is the similarity between ‘A’ and ‘D’ ? 171. a.Why do we classify elements?
f. Identify the most abundant element in the earth b. What were the two criteria used by Mendeleev in
crust. creating his periodic table.
c. Why did Mendeleev left some gaps in his periodic
 table? ionic compound which can also be extracted from sea
d. In Mendeleev’s periodic table, why was there no water. Oxides of the elements A and B are basic in
mention of nobles gases like He, Ne and Ar? nature while those of E and F are acidic. The oxide
e. Would you place two isotopes of Cl-35 and Cl-37 of element D is almost neutral. Answer the following
in different slots because of their different atomic questions based on the information given herein:
mass or in the same slot because their chemical a. To which group or period of the periodic table do
properties are same? Justify your answer. the listed elements belong?
Ans : [CBSE 2015, 2013, 2012] b. Which one of the eight elements is likely to be a
noble gas?
a. It makes their study easier.
c. Which of the eight elements would have the
b. (i) Increasing order of atomic mass, (ii) Formula
largest atomic radius?
of oxides and hydrides.
d. Which two elements amongst these are likely to
c. The gaps were left for the elements to be
be non-metals?
discovered.
e. Which one of these eight elements is likely to be a
d. Noble gases were not invented at that time.
semi-metal or a metalloid?
e. They will be placed at the same slot as they
have the same atomic number and same chemical Ans : [CBSE 2010]
properties. a. A and B belongs to group-1 and. group-2
respectively because they form basic oxides. ‘C’
172. Atoms of eight elements A, B, C, D, E, F, G and H belongs to group-13, ‘D’ belongs to group-14 which
have the same number of electronic shells but different forms almost neutral oxide (actually amphoteric
number of electrons in their outermost shell. It was oxide), E and F belong to group-15, 16 forming
found that elements A and G combine to form an acidic oxides. ‘G’ belongs to group-17 because
ionic compound. This compound is added in a small NaCl is used in cooking. ‘H’ belongs to group 18.
amount to almost all vegetable dishes during cooking. they belong to third period of the periodic table.
Oxides of elements A and B are basic in nature while b. H belongs to noble gas elements.
those of E and F are acidic. The oxide of D is almost c. A will have largest atomic radius.
neutral. Based on the above information answer the d. E and F are likely to be non-metals,
following questions: e. D is likely to be a metalloid or semi metal.
a. To which group or period of the Periodic Table do
the listed elements belong to?
b. What would be the nature of the compound
formed by the combination of elements ‘B’ and
‘F’ ?
c. Which two of these elements could definitely be
metals?
d. Which one of the eight elements is most likely to
be found in gaseous state at room temperature?
e. If the number of electrons in the outermost shell
of elements ‘C’ and ‘G’ be 3 and 7 respectively,
write the formula of the compound formed by the
combination of‘C’and ‘G’.
Ans : [CBSE 2010]
a. A and B belongs to group-1 and group-2
respectively because they form basic oxides. ‘C’
belongs to group-13, ‘D’ belongs to group-14 which
forms almost neutral oxide (actually amphoteric
oxide), E and F belong to group-15, 16 forming
acidic oxides. ‘G’ belongs to group-17 because
NaCl is used in cooking. ‘H’ belongs to group 18.
they belong to third period of the periodic table.
b. B and F will form ionic compound because ‘B’ is
a metal and ‘F’ is a non-metal.
c. A and B are definitely metals.
d. H is most likely to be found in gaseous state at
room temperature.

e. is the formula of compound.

173. Atoms of eight elements A, B, C, D, E, F, G and H

have the same number of electronic shells but different
number of electrons in their outermost shell. It was
, found that elements A and G combine to form an
Chap 8 : How Do Organisms Reproduce www.cbse.online

CHAPTER 8
How Do Organisms Reproduce

ONE MARK QUESTIONS beings.

Ans : [Delhi 2015]
a. Testis produce sperms.
1. Name the method by which Spirogyra reproduce b. Produces male sex hormone, testosterone.
under favourable conditions. Is this method sexual or
asexual? 10. Name the causative organism of the disease “Kala-
Ans : [Delhi 2017] azar” and its mode of asexual reproduction.
Fragmentation. Asexual Ans : [Foreign 2015]
Leishmania, Binary fission.
2. Name the method by which Planaria reproduce
under favourable conditions. Is this method sexual or 11. Name two simple organisms having the ability of
asexual? regeneration.
Ans : [Delhi 2017] Ans : [CBSE 2015]
Regeneration. Asexual Planaria/hydra/earthworm (any two).

3. Name the method by which Plasmodium reproduce 12. Give the respective scientific terms used for studying:
under favourable conditions. Is this method sexual or a. The mechanism by which variations are created
asexual? and inherited and
Ans : [Delhi 2017] b. The development of new type of organisms from
the existing ones.
Multiple Fission. Asexual
Ans : [CBSE 2015]
4. When a cell reproduces, what happens to its DNA? a. Heredity
Ans : [All India 2017] b. Fission.
Its DNA first doubles up followed by its equal and
accurate division between two daughter cells.

5. List two functions of ovary of human female

reproductive system.
Ans : [All India 2016]
In human female, ovary contains thousands of eggs.
One egg is produced every month one of the ovaries.
Ovary also secretes estrogens hormone for development
of sexual characteristics at puberty.

6. What are those organisms called which bear both sex

organs in the same individual. Give one example of
such organism.
Ans : [All India 2016]
13. Give an advantage of vegetative propagation.
Bisexual. For example: earthworm, leech, starfish,
Ans : [CBSE 2015]
hibiscus, mustard. (Any one)
Vegetative propagation can be practised for growing
7. Where is DNA found in a cell? such plants which usually do not produce seeds or
Ans : [CBSE 2016] produce non-viable seeds.
Genes/Chromosomes. 14. Name the type of cells which undergo regeneration.
8. Name the life process of an organism that helps in the Ans : [CBSE 2015]
growth of its population. Regenerative cells can proliferate and make large
Ans : [All India 2015] number of cells.
Reproduction. 15. What are sexually transmitted diseases? Name an
STD which damages the immune system of human
9. List two functions performed by testis in human
 body. Germination: Development of embryo into a seedling.
Ans : [CBSE 2015] Fertilization: Fusion of male and female gametes.
a. Diseases that spread through the sexual contact. 26. Why is sexual reproduction considered to be superior
b. AIDS to asexual reproduction is terms of evolution?
16. Organisms have a varied body design. Name the Ans : [Sample Paper 2010]
property which gives the basic difference in body Sexual mode of reproduction is a source of variation
design. (in a population of organisms) which ensures survival
Ans : [CBSE 2014] of the species.
Errors in DNA copying (variations). 27. Malarial parasite divides into many daughter
individuals simultaneously through multiple fission.
17. How can the chromosomes be identified?
State an advantage the parasite gets because of this
Ans : [CBSE 2014] type of reproduction.
Chromosomes can be seen as thread like structure Ans : [Sample Paper 2010]
when cell is dividing.
a. Progeny is identical like parent and in large
18. Why is temperature of scrotal sac 2°C less than the number.
body temperature? b. Single individual can reproduce.
Ans : [CBSE 2014,12] 28. Name two ways of vegetative propagation practiced
Because testes require temperature 2°C less than the by gardeners.
body temperature for the production of sperms. Ans : [All India 2009]

19. How does the embryo gets nourishment from the Cutting and grafting.
mother?
29. What is reproduction?
Ans : [All India 2013]
Ans : [All India 2009 C]
Through placenta.
Reproduction is the process of producing individuals
20. Why does the lining of uterus become thick and of its own kind.
spongy every month?
30. What is the effect of DNA copying which is not
Ans : [CBSE 2013] perfectly accurate on the reproduction process?
To receive and nurture the growing embryo, lining of Ans : [All India 2008]
uterus become thick and spongy.
Leads to variation/ evolution.
21. Regeneration is not possible in all types of animals.
Why? TWO MARKS QUESTIONS
Ans : [CBSE 2012]
Regeneration is carried by specialised cells. The
31. State the changes that take place in the uterus when
organisms which have those cells only can show
a. implantation of embryo has occurred
regeneration.
b. female gamete/egg is not fertilized
22. What is the advantage of reproducing through spores? Ans : [Delhi 2017]
Ans : [CBSE 2012] a. Uterus wall becomes thicker due to development
In the form of cyst, spore with a cell wall can survive of blood vessels and glands in it and placenta
in adverse conditions. develops from the side of foetus so that it can
derive nutrition from mother and pass the waste
They can be easily dispersed through wind as to mother’s blood.
they are more in number and light in weight. b. Uterus lining gets peeled and shed off along with
23. What happens if egg is not fertilized? mucus, blood, dead ovum during menstruation.
Ans : [CBSE 2012] 32. Give reasons as to why the following processes are
If fertilization does not occur then menstruation different from each other:
occurs, i.e., blood and mucus comes out through the a. Fission in Amoeba and Plasmodium .
vagina. b. Binary fission and Fragmentation.
Ans : [CBSE 2016]
24. Differentiate between pollen grain and ovule.
a. In Amoeba during binary fission the cell divides
Ans : [CBSE 2011]
into two daughter cells while in Plasmodium
Pollen grains contain male gametes and ovules multiple fission occurs, where the cell divides into
contains female gametes in plants. many daughter cells.
b. In binary fission, a cell divides into two daughter
25. Differentiate between germination and fertilization, cells while in fragmentation, the body of a
Ans : [CBSE 2011 ] multicellular organisms divides into two or more
 parts which grow further. a. Each piece grows into a complete organism.
b. Develops into new plants.
33. a. What is the location of the following: c. Changes occurs in the appearance at the time of
(i) DNA in a cell (ii) Gene puberty.
b. Expand DNA.
Ans : [CBSE 2016] 38. What does the diagram given below correctly
illustrate? Give reason in support of your answer.
a. (i) Nucleus. (ii) Located on the chromosomes.
b. Deoxyribo Nucleic Acid.

34. Explain how do organisms create an exact copy of

themselves.
Ans : [CBSE 2016]
To build the copies of DNA or the genetic material,
the cells use biochemical reactions.
Additional cellular apparatus along with the DNA
copies are separated and so a cell divides to give rise Ans : [All India 2014-15]
to two almost identical cells.
Binary fission in Amoeba. The splitting of the two
35. “Variations” are seen in the organisms. State the two cells during division in Amoeba can take place in any
main causes of variation. plane.
Ans : [CBSE 2015] 39. What is the main difference between sperms and eggs
Variations are caused by: of human? Write the importance of this difference?
a. Change in the genetic material, i.e., DNA at the Ans : [All India 2014]
time of DNA copying.
Sperms are motile and are produced in . large
b. Environmental factors viz., light, temperature,
numbers by a male. Egg are non-motile and only one
nutrition, wind and water supply, etc.
is produced at a time by the female.
c. Mutations.
Sperms are motile as they have to travel up to egg
for fertilization. It becomes zygote, remains protected
inside female’s body and gives rise to foetus and baby.

40. Draw labelled diagrams to illustrate budding in Hydra.

Ans : [CBSE 2014]
a. In sexual reproduction, fusion of male and female
gametes takes place, these germ-cells/gametes
contain half the number of chromosomes and by
the fusion of these gametes the zygote is formed
with full set of chromosomes.
b. When male and female gametes fuse at the time
of fertilization, it restores the original number
of chromosomes (of the parent), ensuring the
stability of species.
36. Define the following processes of asexual reproduction:
a. Spore formation 41. “The chromosomal number of the sexually producing
b. Regeneration parents and their offspring is the same.” Justify this
c. Multiple fission statement.
Ans : [CBSE 2015] Ans : [CBSE 2014]

a. Reproduction seen in organisms by formation of a. DNA copying is essential for formation of addition
spores. cellular apparatus, so that when DNA copies
b. Organisms are cut into any number of pieces and separate, each cell gets its own cellular apparatus.
each piece grows into a complete organism. b. The process of DNA copying results in variation
c. Unicellular organisms divide into many daughter each time. As a result, the DNA copies generated
cells simultaneously. will be similar, but may not be identical to the
original.
37. What happens when the following situations are
initiated: 42. “The consistency of DNA copying during reproduction
a. A Planaria is cut into three different pieces. is important for the maintenance of body design
b. Leaf of the Bryophyllum with notches falls on the features.” Support this statement with two arguments.
soil. Ans : [CBSE 2014]
c. Testosterone is released in the male reproductive
system. 43. Why is vegetative propagation practised for growing
Ans : [CBSE 2015]
 some types of plants? [Delhi 2012] a. Formation of sperms takes place in testes.
or b. Prostate gland contributes fluid to the semen.
Why is vegetative propagation practiced for growing
some types of plant? List two plants which are grown 50. Why do we need to adopt contraceptive measures?
by this method. Ans : [CBSE 2012, 13]
Ans : [All India 2013] a. Contraceptive measures are needed to be adopted
Advantages of vegetative propagation: to prevent unwanted pregnancies.
a. The plants bear flowers and fruits earlier than b. To prevent sexually transmitted diseases.
those propagated sexually. c. Spacing between children.
b. Plants have lost capacity to form seeds hence d. For sound health of a mother.
they are propagated vegetatively. Such plants are
51. Give two differences between a male and a female
genetically similar to parent plants and have all
gamete.
their characters.
Ans : [CBSE 2012]
44. Define variation in relation to a species. Why is a. Male gamete is smaller in size or compared to the
variation beneficial to the species? female gamete.
Ans : [CBSE 2013] b. Male gamete is motile whereas female gamete is
Variation means certain changes which occur in non-motile.
sexually reproducing organisms because of errors in
52. What kind of contraceptive methods prevents STDs
DNA copying. Variations are beneficial for species
and how?
because they given survival advantage even in the
adverse environmental conditions. Ans : [CBSE 2012]
Barrier method prevent STDs.
45. State the importance of chromosomal difference By this method there is no direct contact of genital
between sperms and eggs of humans. organs of male and female and thus it prevents
Ans : [CBSE 2013] transmission of any infection.
Eggs always contain same type of sex chromosomes
53. List any two reasons why the Government has banned
(both X). Sperms contain X or Y sex chromosomes.
prenatal sex determination by law.
Thus, sperm containing X chromosome when combines
with X chromosome of egg results in a female child. Ans : [CBSE 2012]
Whereas sperm containing Y chromosome when a. People may get female foetus aborted.
combines with X chromosome of egg results in a male b. Reckless female foeticide has disturbed male-
child. female ratio in society.

46. a. List any two methods of asexual reproduction. 54. Mention any four ways of asexual reproduction.
b. Explain how Spirogyra reproduces. Ans : [CBSE 2012]
Ans : [CBSE 2013]
a. Fission
a. (i) Budding in Hydra and Yeast. b. Budding
(ii) Spore formation in Fungi. c. Spore formation
b. Spirogyra breaks up into smaller pieces upon d. Fragmentation
maturation. These fragments grow into new e. Regenerations
individuals
55. Mention the functions of (a) placenta (b) fallopian
47. How can pregnancy be prevented surgically? tube in the human female , reproductive system.
Ans : Ans : [CBSE 2012]
Pregnancy can be prevented surgically by adopting: a. Placenta:
a. Vasectomy: When vas deferens in males are blocked (i) Helps in transporting glucose and oxygen
surgically, sperm transfer will be prevented. from the mother to the embryo.
b. Tubectomy: When fallopian tubes are blocked, (ii) Waste generated by the embryo is removed by
eggs will not be able to reach the uterus. transferring it to the mother’s blood.
b. Fallopian tube:
48. ‘Regeneration is not reproduction’. Justify this (i) Helps in carrying the egg from the ovary to
statement with reason. the uterus.
Ans : [CBSE 2013,14] (ii) Fertilization occurs here.
When a piece is cut from an organism, it grows into
56. List any four modes of asexual reproduction.
complete organisms. Regeneration is carried out by
specialized cells. It is not reproduction since most Ans : [All India 2011]
organisms would not be able to grow through pieces. a. Four modes of asexual reproduction:
b. Fission
49. State one function each performed by the following c. Budding
organs in human beings: (a) Testes (b) Prostate gland d. Spore formation
Ans : [CBSE 2013] e. Fragmentation
 f. Regenerations c. ovule
d. sepals and petals
57. Give one example each of a unisexual and bisexual
Ans : [CBSE 2011]
flower. [All India 2011]
or a. forms zygote
Differentiate between unisexual and bisexual flower. b. forms fruit
or c. forms seed
Distinguish between unisexual and bisexual flowers d. shrinks and fall off
giving one example of each.
62. What is the function of copper-T used by some
Ans : [All India 2014-15] women? What is its effect?
Unisexual flower have only one type of sex organ, Ans : [CBSE 2011 ]
either carpels or stamen, hence they are either male
Copper-T prevents pregnancy as it prevents
or female flower. For example: Cucurbit and maize.
implantation in the uterus. It can cause side effect
Bisexual flower have both carpels and stamens. For
due to irritation of the uterus.
example: Marigold and rose.
63. Leaves of Bryophyllum fallen on the ground produce
58. List any two differences between pollination and
new plants. Why?
fertilization.
Ans : [CBSE 2011]
Ans : [CBSE 2011]
Leaves of Bryophyllum bears adventi¬tious buds/
Pollination Fertilization plantlets in the notches along the leaf margin. When
1. It is the transfer of It is the fusion of male the buds fall on the soil they develop into new plant
pollen grain from gamete with female under favourable condi-tions.
the anther to the gamete (egg).
64. Differentiate between self-pollination and cross-
stigma of flower.
pollination.
2. It is achieved by It is achieved by the Ans : [CBSE 2011]
agents like wind, growth of pollen tube
water or animals. so that the male Self-pollination Cross-pollination
gamete reaches the
1. Self-pollination is Cross-pollination is
female germ cells.
the transfer of pollen the transfer of pollen
3. It leads to It leads to formation of grains from anther grains from anther
fertilization. seeds to stigma within the to stigma in another
4. It is an external It is an internal same flower. flower.
process process. 2. It occurs either in It occurs between
the same flower or two flowers which are
59. Differentiate between plumule and radicle. another flower of the on different plants
Ans : [CBSE 2011] same plant. but are of the same
species.
Plumule Radicle
3. It occurs in the It occurs between
1. The part of growing The part of growing flowers which are flowers which are
embryo which later embryo which later form genetically same. genetically different.
forms the shoot of the root of young plant.
young plant. 65. Label any four parts.
2. It is positively It is positively
phototrophic geotrophic and
and negatively negatively phototrophic.
geotrophic.

60. Name the type of asexual reproduction in:

a. Planaria
b. Rhizopus
c. Spirogyra
d. Hydra
Ans :
a. Regeneration
b. Spore formation
c. Fragmentation
d. Budding Ans : [Sample Paper 2010]
1. Stigma 2. Anther 3. Style 4. Filament 5. Petal
61. What happens to the following parts after fertilization?
6. Ovary 7. Sepal (any four)
a. ovum
b. ovary
66. What are the functions of the following in male
reproductive system?
a. Seminal vesicles
b. Prostate gland
Ans : [All India 2009]
a. In human males, seminal vesicles store sperms
temporarily before ejaculation.
b. Both seminal vesicles and prostate gland add
their secretions so that the sperms remain in a
fluid which makes their transport easier and also
this fluid provides nutrition.

69. Draw a labelled diagram of

a. Spore formation in Rhizop us
b. Multiple fission in Plasmodium.
Ans : [CBSE 2008 C]

67. Draw a labelled diagram of

a. Regeneration in Planaria
b. Budding in Hydra [CBSE 2008 C]
or
Explain budding in Hydra with the help of labelled
diagrams only.
Ans : [Delhi 2015]

70. Write two differences between binary fission and

multiple fission in a tabular form as observed in the
cells of the organisms.
68. Draw a labelled diagram of (i) Binary fission in
Ans : [All India 2008, 2010]
Amoeba (ii) leaf of Bryophyllum with buds.
Ans : [CBSE 2008 C] Binary Fission Multiple Fission
1. One cell splits into One cell divides into
two equal halves. many daughter cells
simultaneously
 Binary Fission Multiple Fission Define reproduction. How does it help in providing
stability to the population of species?
2. Each nuclear division Nuclear division Ans : [CBSE 2015 C]
is followed by occurs several times,
cytoplasmic division. they move towards the a. Reproduction is the process of producing
It can be irregular, periphery followed by individuals of its own kind. Through reproduction,
longitudinal or cytoplasmic division. the continuity is maintained.
transverse. b. Members of population are eliminated due to old
age, disease, accidents and other reason. They
3. Generally seen during Generally occurs have to be replaced by new members in order to
favourable conditions in unfavourable maintain a stable population.
e.g., Many bacteria conditions or in c. Reproduction brings variation so that population
and Protozoa like, parasitic forms e.g., may adapt better and evolution in species takes
Amoeba, Paramecium Plasmodium (malarial place. Ultimately new species originate from pre-
and Leishmania. parasite) existing ones.
d. Reproduction is not essential for an individual
THREE MARKS QUESTIONS as its survival is not dependent upon it but is
essential for a species for its survival.

71. What is vegetative propagation? List two advantages 74. Mention the total number of chromosome along
and two disadvantages of vegetative propagation. with sex chromosome. Explain how in a sexually
reproducing organism chromosome number of parents
Ans : [All India 2017]
and their offsprings is the same.
Method of producing new plants from vegetative Ans : [Delhi 2017]
parts like roots, stem and leaves is called vegetative
propagation. Total number chromosomes is 23 pairs. The last pair
Advantages are: is called sex chromosome. If they are similar, they are
a. The plants bear flowers and fruits earlier than termed as XX chromosome. They are present in the
those propagated sexually. females. If they are dissimilar, they are called XY.
b. Plants have lost capacity to form seeds hence they They are present in the males. DNA doubling is always
are propagated vegetatively. followed by cell division. But multicellular organisms
Disadvantages are: have special linkages of cells in specialised organs
a. Such plants are genetically similar to parent plants which have only half the number of chromosomes and
and are vulnerable to infections and diseases. half the amount of DNA. Thus, when these germ-
b. They do not have variations therefore do not cells from two individuals combine during sexual
adapt well to changing environment, the plant reproduction to form a new individual, it results in
species does not evolve. re-establishment of number of chromosome and DNA
content.
72. List three techniques to prevent pregnancy. Which of
them is not meant for males? How does the use of such 75. State the basic requirement for sexual reproduction.
techniques have an impact on health and prosperity of Write the importance of such reproduction in nature.
a family? [All India 2017] Ans : [Delhi 2017]
or Sexual reproduction takes place in multicellular
List any four methods of contraception used by organisms with complex body design. There are
humans. How does their use have a direct effect on specialized (sex) organs in which through a special
the health and prosperity of a family? type of cell division, number of chromosome is reduced
Ans : [Delhi 2015, All India 2014] to half and male and female germ cells/gametes form.
Three techniques to prevent pregnancy: These gamete fuse to form zygote on fertilization,
a. Mechanical barrier — male or female. thus the characteristic number of chromosome and the
b. Taking oral pills/i-pill/saheli - changing the normal DNA content for a cell is regained.
hormonal balance of the body so that eggs are Sexual reproduction gives rise to more variations
not released. which are essential for evolution as well as survival
c. Use of the loop or the Copper-T. of species under unfavorable conditions. Species
d. Surgical method - tubectomy / vasectomy reproducing sexually have better chances of survival.
Use of hormonal preparations is not meant for
males. 76. What happens when:
Effect on Health and Prosperity: a. Accidentally Planaria is cut into three different
a. Health of women is maintained pieces.
b. Parents can give more attention to children b. Bryophyllum leaf fall on the wet soil.
c. More resources can be made available. c. On maturation sporangia of Rhizopus burst.
Ans : [Delhi 2017]
73. Reproduction is one of the most important
characteristics of the living beings. Give three reasons a. Three new Planaria will form due to regeneration.
in support of your answer. [All India 2017] b. New plantlets will form from these buds helping
or the plant to propagate vegetatively.
 c. Spores are released which upon finding suitable flower by agents like wind, water or animals.
substratum germinates to form new individual. c. Style is the middle elongated part of the carpel.
It acts as a passage for pollen to reach ovary for
77. List four steps in sexual reproduction. Write two of the fertilization. Filaments is the elongated part
its advantages. of stamen.
Ans : [Delhi 2017]
81. a. Trace the path of sperms from where they are
a. Four steps in sexual reproduction :
produced in human body to the exterior.
b. Formation of gametes in the sex organs.
b. Write the functions of secretions of prostate gland
c. Transfer of male gamete to female gamete which
and seminal vesicles in humans.
involves release of both types of gametes in the
medium outside. Ans : [CBSE 2016]
d. Fusion of gametes, either inside or outside the a. The formation of sperms takes place in testes and
female parents body. delivered through the vas deferens which unites
e. Development of zygote to embryo and then with a tube coming from urinary bladder to form
complete individual. urethra from where they are excreted out of the
Advantages: body.
a. Variations are produced among the progeny. b. Prostate gland and seminal vesicles add their
b. Such populations are able to adapt well to secretions to make the sperms motile in a fluid
changing environment and thus evolves faster. which makes their transport easier and provides
nutrition.
78. Write one main difference between asexual and sexual
mode of reproduction. Which species is likely to 82. Give two examples each of the following:
have comparatively better chances of survival - the a. Plants having unisexual flowers
one reproducing asexually or the one reproducing b. Agents of pollination
sexually? Give reason to justify your answer. c. Physical changes on puberty that are common to
Ans : [CBSE 2017] both boys and girls.
Ans : [CBSE 2016]
Sexual reproduction Asexual reproduction
a. Papaya, watermelon
1. It involves two parents It involves only one b. Insects, air, water, etc.
and causes genetic parent and does c. (i) Appearance of pubic hair.
variation. not causes genetic (ii) Skin becomes oily and may develop pimples.
variation.
83. Why are the testes located outside the abdominal
2. Fertilization/zygote No fertilization/zygote
cavity? Mention the endocrine and exocrine function
formation is observed. formation is observed.
of testes.
The species having sexual mode of reproduction Ans : [CBSE 2016]
have better chances of survival because sexual
reproduction leads to variations which give better Sperm formation requires a lower temperature than
survival advantage to the species over time. the normal body temperature. This temperature is
1-3°C lower than the temperature of the body. Testes
79. Explain the term “Regeneration” as used in relation are thus located outside so that scrotum provides an
to reproduction of organisms. Describe briefly how optimal temperature for the formation of the sperms.
regeneration is carried out in multicellular organisms Endocrine function:
like Hydra. Production of male hormone (testosterone).
Ans : [All India 2016] Exocrine function:
Production of male gametes (sperms).
The ability to give rise to new individuals from
the body parts of the parent individual is called 84. List six specific characteristics of sexual reproduction.
regeneration, e.g., Hydra and Planaria, if their bodies Ans : [All India 2015, CBSE 2016]
get broken into many pieces, each piece is capable of
re-growing into a complete individual. Characteristics of sexual reproduction:
a. Two parents are involved.
80. Compare the following: b. Two dissimilar gametes are formed by meiosis.
a. Unisexual and bisexual flower. c. Variations are produced.
b. Self-pollination and cross pollination. d. Occurs in all the higher and some of the lower
c. Style and filament. organisms.
Ans : [All India 2016-17] e. Fertilization / fusion of gametes leading to zygote
formation.
a. Unisexual flowers have either stamens or carpels,
e.g., Papaya and Watermelon. Bisexual Flowers 85. List four points of significance of reproductive health in
have both stamens and carpels, e.g., Mustard and a society. Name any two areas related to reproductive
Hibiscus. health which have improved over the past 50 years in
b. Self-Pollination is transfer of pollen grains from our country.
the stamen to the stigma of same flower. Cross Ans : [All India 2015, CBSE 2016]
Pollination is transfer of pollen grains to another
 Significance: a. Barrier method (Condoms)
a. Prevent STDs. b. Surgical method (Vasectomy in males and
b. Advantage of small family. Tubectomy in females)
c. Less mortality among new-borns. c. Withdrawal method
d. Reduces the cases of maternal mortality. d. Calendar method
Areas which have improved: e. Hormonal method
a. Family Planning. f. IUCD/Copper-T/Loop (any four)
b. Decrease in STD cases. Two advantages:
a. Helps in maintaining health of women.
86. What is placenta? Explain its function in human b. Helps in preventing STDs especially AIDS.
female. [Foreign 2015, All India 2014] c. Helps in birth control.
or
State the role of placenta in the development of
embryo. [All India 2013]
or
What is placenta? Describe its structure. State its
functions in case of a pregnant human female.
Ans : [All India 2016]
Placenta is a specialized tissue embedded in the
uterine wall. It contains villi on the embryo’s side and
blood spaces on the mother’s side.
Function:
a. Helps in passing of nutrients from mother to
foetus.
b. Exchange of oxygen and carbon dioxide gases.
c. Passing of waste materials from embryo to the
mother. 90. List any two modes of asexual reproduction. Under
which mode of reproduction is vegetative propagation
87. Write one main difference between asexual and sexual placed and why? List two advantages of vegetative
mode of reproduction. Which species is likely to propagation.
have comparatively better chances of survival- the Ans : [All India 2014]
one reproducing sexually or the one reproducing
asexually? Justify your answer. Two modes of asexual reproduction are fission
[Foreign 2015, All India 2018] Regeneration
or Vegetative propagation is placed under asexual
How is sexual reproduction better than asexual reproduction as reproduction happens from any part
reproduction? of a plant. It may be either leaf, shoot or root.
Ans : [All India 2013] Advantages are:
a. Asexual reproduction does not involve genetic a. The plants bear flowers and fruits earlier than
fusion while sexual reproduction involves fusion of those propagated sexually.
male and female gametes to form a zygote. b. Plants have lost capacity to form seeds hence they
b. Species reproducing sexually have better chances are propagated vegetatively.
of survival. 91. “Regeneration is not same as reproduction”.
Reason : a. Justify the statement.
Sexual reproduction gives rise to more variations b. What is meant by regeneration?
which are essential for evolution as well as survival c. How is this process different from
of species under unfavorable conditions. fragmentation?
88. What are chromosomes? Explain how in sexually Ans : [All India 2015]
reproducing organisms, the number of chromosomes a. Regeneration is not the same as reproduction,
in the progeny is maintained? since most organisms would not normally depend
Ans : [CBSE 2015] on being cut up to be able to reproduce.
Chromosomes are thread like structures made-up of b. The ability to give rise to new individuals from
DNA found in the nucleus. The original number of the body parts of the parent individual is called
chromosomes becomes half during gamete formation. regeneration.
Hence, when the gametes combine, the original c. In fragmentation, the body of a simple multicellular
number of chromosome gets restored in the progeny. organism breaks down onto many ‘fragments’. All
cells undergo division and the organism develops
89. List four categories of contraceptive methods. State from each fragment. Regeneration occurs only
in brief two advantages of adopting such preventive through some specialised cells.
methods.
92. Explain the process of regeneration in Planaria. How
Ans : [CBSE 2015] is this process different from reproduction?
Four categories of contraceptive methods are: Ans : [All India 2014, CBSE 2008]
 Regeneration is the ability to give rise to new a. Binary fission.
individuals from the body parts of the parent b. Amoeba.
individual e.g., Hydra and Planaria, if their bodies c. Binary fission occurs in unicellular organisms
get broken into many pieces, each piece is capable of only. In fragmentation the body of a simple
re-growing into a complete individual. multicellular organism breaks down into many
‘fragments’. All cells undergo division and the
organism develops from each fragment.

95. DNA content has the tendency to double itself during

sexual reproduction due to combining of the genetic
materials from the two parents. How the problem
of DNA doubling can be solved to maintain the
consistency of the genetic material throughout the
species?
[All India 2014-15]
or
“The chromosome number of the sexually reproducing
parents and their offsprings is the same”. Justify the
statement.
Ans : [All India 2014]
In some organism regeneration occurs but only DNA doubling is always followed by cell division. Due
to regain lost body parts like in tail of lizard, arm to this special cell division, gametes form with half the
of a star fish. In the case of Planaria, it is a way of content of DNA and single set of chromosomes. These
reproduction that is producing organisms of its own gamete fuse to form zygote on fertilization. Thus the
kind. characteristic number of chromosome and the normal
DNA content for a cell is regained.
93. In the process of reproduction as used by Spirogyra,
Thus the consistency of the genetic material
the organism splits itself into small pieces.
throughout the species is maintained and for the
a. What is this process of reproduction called?
same reason the chromosome number of the sexually
b. Is this type of reproduction sexual or asexual?
reproducing parents and their offsprings is the same.
Answer with reason.
c. Is this process same as regeneration?
Ans : [All India 2014-15] 96. Explain the structure of the female reproductive
a. Fragmentation. system of humans.
b. Asexual as only one parent is involved, Ans : [All India 2014-15]
c. In fragmentation, the body of a simple multicellular Female Reproductive System consists of ovaries,
organism breaks down into many ‘fragments’. All fallopian tubes, uterus and vagina.
cells undergo division and the organism develops a. Ovaries are located inside the abdominal cavity,
from each fragment. near the kidney. It performs two functions:
In regeneration, body of a multicellular • Produce female germ - cells/eggs. Every
organism get broken into many pieces, each piece month one egg is produced
is capable of re-growing into a complete individual. • Secrete hormones like Estrogens which
stimulate the development of secondary
94. Study the diagram given below:
sexual characteristics at puberty.
b. Fallopian Tubes carry the egg from ovary to the
womb; egg gets fertilized in the oviducts only if it
meets a sperm.
c. Uterus is a elastic bag like structure. The fertilized
egg, the zygote gets implanted in the fining of
uterus and develops into an embiyo.
d. Vagina (Birth Canal) receives the sperms as well
as child is borne through it.

a. Identify the process. 97. Give the functions of the following in the process of
b. Which organism uses the above method of reproduction:
reproduction? a. Pollen tube.
c. How is the above method different from the b. ovary,
process of fragmentation? [All India 2014-15] c. Stigma.
or Ans : [All India 2015]
In context of reproduction of species, state the main
difference between fission and fragmentation. Also a. Pollen tube carries male gamete from stigma to
give one example of each. ovule.
b. Ovary has ovule and forms fruit to protect and
Ans : [All India 2016]
dispersal of seeds.
 c. Stigma receives pollen during pollination. formation of zygote is known as fertilization.
The growth of embryo (present in the seed)
98. Justify the following statements: into seedling under appropriate conditions is
a. Variation is beneficial for the species over a period known as germination.
of time.
b. New offsprings produced are similar to their 102. A part of the male reproductive system is shown
parents but not identical. below. Study the diagram and answer the questions
c. Binary fission is different in Amoeba and that follow.
Leishmania.
Ans : [All India 2014-15]
a. Variations help a population in the process of
natural selection and accumulation of adaptations
in a population. It leads to evolution of a species.
b. Offspring, especially when produced sexually, have
minor differences or variations among themselves
hence they may not look identical. By virtue of
them being from same species they look similar.
c. Binary fission in Amoeba is in any plane but in
Leishmania it is in a fixed plane.

99. What happens when:

a. APlanaria is cut into three different pieces,
b. Leaf of the Bryophyllum with notches fall on the
soil.
c. Testosterone is released in the male reproductive a. Two part have been incorrectly labelled. Identify
system. them.
Ans : [All India 2014-15] b. Give the function of urethra.
c. Which hormone is released by testis?
a. Three new Planaria will form due to regeneration.
Ans : [CBSE 2014]
b. New plantlets will form from these buds helping
the plant to propagate vegetatively. a. Testis, penis.
c. The male shows masculine features and attains b. Urethra serves as a common passage for both
fertility. Sperm starts forming in testis. sperms and urine.
c. Testosterone.
100. What is the effect of DNA copying, which is not
perfectly ccurate, on the reproduction process? How 103. Mention one function each of the following parts with
does the amount of DNA remain constant though respect to the female reproductive system:
each new generation is a combination of DNA copies a. Vagina
of two individuals? b. Ovary
Ans : [CBSE 2014] Ans : [CBSE 2014]
a. DNA copying leads to more variations in the a. The uterus open into vagina through the cervix.
offspring. The sperms enter through the vaginal passage
b. Sexually reproducing organisms have special during sexual intercourse.
lineage of cells which have only half the number b. One egg (female gamete) is produced every month
of chromosomes as the parent cell. by one of the ovaries.
c. When such germ cells fused, a new individual is
104. List and explain in brief three methods of contraception.
formed with the same amount of DNA as that of
[All India 2013]
parent.
or
101. Differentiate between the following: List any four methods of contraception. How are they
a. Placenta and uterus helpful to young couples?
b. Unisexual and bisexual flowers Ans : [All India 2014]
c. Fertilization and germination Four methods of contraception:
Ans : [CBSE 2014] a. Condoms
a. Placenta and uterus : The embryo gets nutrition b. Copper-T
from the mother’s blood with the help of a special c. Diaphragm
tissue called placenta. d. Oral pills
After fertilization, embryo gets attached to All these help in family planning as it helps in
the walls of uterus. keeping gap between two children. They help in proper
b. Unisexual flowers contain either stamens or utilization of family resources.
carpels. Bisexual flowers contain both stamens
and carpels. 105. Write scientific name for malarial parasite. How
c. Fertilization and germination : The fusion of is fission in amoeba different from that of malarial
male gamete with female gamete leading to the
 parasite? (ii) Use covering on vagina.
Ans : [All India 2013]
110. a.How do organisms reproduced by fission?
a. Plasmodium, b. Write names of any two organisms which reproduce
b. Fission in amoeba produces two daughter cells by this method.
- binary fission. Fission in Plasmodium produce c. Differentiate between the fission of Leishmania
many daughter cells - multiple fission, and Plasmodium.
106. a.Give the functions of the following: Ans : [CBSE 2013]
1. Pollen tube a. Cell division takes place which leads to creation of
2. Ovary new individuals.
b. List any two changes observed in the body of a b. Bacteria, Protozoa.
female during puberty. c. Leishmania — binary fission occurs in a definite
Ans : [CBSE 2013] orientation.
Plasmodium — undergoes multiple fission,
a. (i) Transfer of male gamete. (ii) Production of
female gamete. 111. Give reasons:
b. (i) Growth of mammary glands. (ii) Onset of a. Wind acts as a pollinating agent.
menstrual cycle. b. Variation is essential and beneficial to a species.
c. Use of condoms prevents pregnancy.
107. What is meant by DNA copying? Mention its
importance in reproduction. Ans : [CBSE 2013]
Ans : [CBSE 2013,14] a. Transfer of pollen grains from anther to stigma.
b. Helps in evolution and survival.
Cells use chemical reactions to build copies of their
c. Prevents fertilization - Barrier method.
DNA. This creates two copies of the DNA in a
reproducing cell. DNA copying is accompanied by 112. What are secondary sexual characters in humans?
the creation of an additional cellular apparatus to Name one such character of male and female.
facilitate the DNA copies to separate with its own Ans : [CBSE 2013]
cellular apparatus. DNA copying gives rise to some
inbuilt tendency for variation during reproduction The characters which distinguish a male from female
which is the basis for evolution. are called secondary sexual characters.
Secondary sexual characters of male are moustache,
108. Distinguish between the functions of ovary and testis.
beard, thick growth of hair on body, strong muscles
Ans : and harsh voice.
Ovary Testis Secondary sexual characters of female are less hair
on body, broad hips, development of breasts and soft
1. Ovary is the primary Testis is the voice.
sex organ in females primary sex organ
which produces eggs in males which 113. Name and explain the method by which Rhizopus
produces sperms. reproduces.
2. It also secretes hormone It also secretes Ans : [CBSE 2013]
such as estrogen hormone Rhizopus reproduces by spore formation. Method: It
(which imparts female testosterone which is a method of asexual reproduction.
secondary sexual imparts male
characters) and secondary sexual
progesterone (which characters.
maintains
pregnancy).
3. Ovary remains Testis remains
functional up to 50 functional even
years of age. more than 70 years
of age.

109. a.What are sexually transmitted diseases? Name

any one which is caused by bacteria and one
caused by viral infection. Spores are produced in a structure called sporangium.
b. Mention any two methods to avoid such diseases.
114. a.Give the functions of: (i) Stigma (ii) Ovary
Ans : [CBSE 2013]
b. State in brief the formation of seed in a flower.
a. Diseases that spread through the sexual contact Ans : [CBSE 2011]
are called sexually transmitted diseases.
(i) Gonorrhoea or syphilis is caused by bacteria. a. (i) The sticky terminal part of the carpel is called
(ii) Warts, HTV, AIDS is caused by virus. stigma. It receives pollen.
b. (i) Use of condoms on penis. (ii) The swollen bottom part of the carpel is
called ovary. It contains female germ cells
 which form seed after fertilization. they be prevented?
b. After fertilization, the zygote divides several times Ans : [All India 2008]
to form an embryo within the ovule. The ovule
a. Bacterial infections: Syphilis, Gonorrhoea.
develops a tough coat and is gradually converted
Viral infections: Warts, AIDS, Hepatitis B,
into a seed.
Herpes.
115. In the diagram of human male reproductive system b. Spread of these diseases can be prevented by
given below: using physical barrier, avoiding sex with multiple
partners.

FIVE MARKS QUESTIONS

a. Label parts A and B.
118. Name the type of asexual reproduction demonstrated
b. Name the hormone produced by organ “X’. What
is the role of this hormone in human male? by the following organisms:
c. Mention the name of substances that are a. Amoeba
transported by tubes (i) C and (ii) D. b. Rhizopus
c. Planaria
Ans : [CBSE 2011]
d. Plasmodium
a. A - seminal vesicle, B - prostate gland. e. Bryophyllum
b. Testosterone: It controls gamete formation/ Ans : [All India 2016-17]
secondary sex organs/ accessory glands.
c. C - sperms, D - sperms/semen and urine. a. Binary fission
b. Spore formation
116. a.Identify the asexual method of reproduction in c. Fragmentation
each of the following organisms: d. Multiple fission
(i) Rose (ii) Yeast (iii) Planaria e. Vegetative propagation
b. What is fragmentation? Name a multicellular
119. Answer the following:
organism which reproduces by this method.
a. How is zygote formed?
Ans : [CBSE 2011]
b. State the function of placenta in the mother’s
a. (i) Vegetative propagation by stem. body.
(ii) Budding c. At what interval the egg is formed in human
(iii) Regeneration female ovary?
b. Fragmentation is a asexual method of reproduction d. Name two STDs caused by bacterial infection.
in which an organism simply breaks up into smaller e. Why is prenatal sex determination prohibited?
pieces/ fragments upon maturation. These pieces Ans : [All India 2017]
or fragments grow into new individuals. Spirogyra
is the multicellular organism with relatively a. Zygote is formed by the fusion of male and female
simple body organisation which reproduces gamete.
through this simple method of reproduction, i.e., b. Placenta is a special tissue through which the
fragmentation. developing embryo/foetus gets nutrition from
mother’s blood. It also transports wastes of the
117. a.Give one example each of sexually transmitted embryo into mother’s blood.
diseases in each of following cases c. Ovulation releases mature ovum from ‘ the ovary.
(i) Bacterial infections (ii) Viral infections It happens once during a menstrual cycle that is
b. How can spread of these diseases be prevented? for roughly 28 days.
[All India 2011] d. STDs caused by bacterial infection are Gonorrhoea
or and Syphilis.
Name one sexually transmitted disease each caused e. Prenatal sex determination is misused and it may
due to bacterial infection and viral infection. How can be the reason for female foeticide.
120. a. List two reasons for the appearance of variations which when fall on the soil, develop into new
among the progeny formed by sexual reproduction. plants.
b. Cutting: A piece of stem, root, leaf or even a bulb
scale is placed partly under moist soil which grows
into a new plant, e.g., rose.
c. Layering: A part of the stem is pulled out and
buried in the soil. The layered stem grows into a
new plant, e.g., Pudina.
d. Grafting: In grafting, two parts from two different
plants are joined together so that they can unite
and grow into a new plant, e.g., sugarcane.

123. a.(i) Write full form of DNA.

(ii) State the role of DNA in the cell nucleus,
(iii) What will be the after effect if the information
of the DNA is changed.
b. Explain the importance of DNA copying in
b. (i) Name the part marked A in the diagram.
reproduction.
(ii) How does “A” reaches part B?
(iii) State the importance of , the part C. Ans : [CBSE 2016]
(iv) What happens to the part marked D after a. (i) Deoxyribo Nucleic Acid.
fertilization is over? (ii) Informational source for making proteins.
Ans : [All India 2016] (iii) Proteins will be changed.
b. Its only due to DNA copying that body designs
a. Sexual reproduction confers new characteristics
are similar because DNA cell nucleus carries
on the offspring due to genetic recombination
information for making proteins if DNA copying
occurring during gamete formation in the sex
will not take place then body design will change.
organs. Moreover it involves union of two gametes
coming from two parents which different genetic 124. List five distinguishing features between sexual and
combination. Thus it ensures more diversity in asexual types of reproductions in tabular form.
characteristics.
Ans : [CBSE 2016]
b. (i) Pollen
(ii) Pollination Sexual reproduction Asexual reproduction
(iii) Pollen tube carries male gametes to the ovule
in ovary. 1. It involves two parents It involves only one
(iv) Ovule turns into seeds. and causes genetic parent and does
variation. not causes genetic
121. Identify the following methods and giving one example variation.
of each: 2. Fertilization/zygote No fertilization/zygote
a. Process in which reproduction takes place by formation is observed. formation is observed.
breaking up of parent into fragments.
b. Process of dividing of organisms into many cells 3. Gametes are formed in No gametes are
simultaneously. both males (sperms) produced.
c. Process of reproduction by formation of bud on and females (ova).
parent body. 4. Meiosis occurs during Meiosis does not
d. Process of reproduction by formation of spores. gamete formation. occur at any stage of
e. Process used by multicellular organisms to reproduction.
reproduce by cutting into many pieces each piece
5. Genetic variation Genetic variation does
forms a new individual.
occurs. not occur.
Ans : [CBSE 2016]
a. Fragmentation, Spirogyra 125. a.Name the human male reproductive organ that
b. Multiple fission, Plasmodium produces sperms and also secretes a hormone.
c. Budding, Hydra Write the functions of the secreted hormone.
d. Spore formation, Rhizopus b. Name the parts of the human female reproductive
e. Regeneration, Planaria. system where
(i) Fertilization takes place,
122. How does vegetative propagation occur in nature? (ii) Implantation of the fertilized egg occurs.
Explain with four different examples. Explain how the embryo gets nourishment
Ans : [CBSE 2016] inside the mother’s body.
There are many plants in which parts like the root, Ans :
stem and leaves develop into new plants under a Testis - secrete male hormone - testosterone.
appropriate conditions. This is called as vegetative Functions : (i) Formation of sperms, (ii)
propagation. Examples of vegetative propagation: Development of secondary sexual characters.
a. Adventitious buds: In Bryophyllum, adventitious b. (i) fallopian tube/oviduct. (ii) uterus.
buds grow in the notches along the leaf margin,
 Placenta is a special disc like tissue embedded (ii) Nourishment of developing embryo.
in the mother’s uterine wall and connected to the b. Placenta is a special disc like tissue embedded in
foetus/embryo. Placenta provides a large surface area the mother’s uterine wall and connected to the
for glucose and oxygen/ nutrients to pass from the foetus / embryo.
mother’s blood to the embryo/ foetus. Placenta provides a large surface area for glucose
and oxygen/nutrients to pass from the mother’s
126. a. Identify A,B,C and D in the given diagram and blood to the embryo/ foetus.
write their names.
128. Differentiate between:
a. Pollen tube and Style
b. Fission of Amoeba and Plasmodium
c. Fragmentation and regeneration
d. Bud of Hydra and bud of Bryophyllum
e. Vegetative propagation and spore formation.
Ans : [All India 2015]
a. Pollen tube forms and male gametes are carried
by it to the ovule.
Style is part of female part- carpel through
which pollen tube passes.
b. Amoeba shows binary fission where one cell splits
into two equal halves.
Plasmodium (malarial parasite) shows
b. What is pollination? Explain its significance. multiple fission where one cell divides into many
c. Explain the process of fertilization in flowers. daughter cells simultaneously.
Name the parts of flower that develop after c. Fragmentation occurs in multi-cellular organisms
fertilization into (i) seed (ii) fruit with simple body organisation like Spirogyra (a
Ans : [Foreign 2015, CBSE 2017, All India 2014,] filamentous alga). It involves breaking up of a
a. A - pollen grain; B - stigma; C - Pollen tube, D - filament into many fragments and each fragment
Female germ cell/Egg cell. growing into new individual.
b. Pollination - Transfer of pollen grains from anther Regeneration is the ability to give rise to new
to the stigma of a flower. individuals from the body parts of the parent
Significance of pollination - Process of pollination individual, e.g., Hydra and Planaria, if their
leads to fertilization as it brings the male and bodies get broken into many pieces, each piece is
female gametes together for fusion. capable of regrowing into a complete individual.
c. After a pollen falls on a suitable stigma, the pollen d. In Hydra, a bud is formed at a specific site by
tube grows out of the pollen grain and travels repeated cell division and develops into a tiny
through the style to reach the ovule in the ovary. hydra.
Here the male germ cell (carried by the pollen In Bryophyllum, vegetative buds arise from
tube) fuses with the female germ cell to form a the notches of its leaves and develops into a new
zygote. plantlet.
e. Vegetative Propagation is the development of new
127. a.Write the function of following parts in human plants from parts like root, leaf and stem under
female reproductive system: (i) Ovary (ii) Oviduct suitable conditions, e.g., Bryophyllum vegetative
(iii) Uterus buds arise from the notches of its leaves. In potato,
b. Describe in brief the structure and function of ginger, garlic etc. it occurs through stems.
placenta. Spore formation: A spore is a special cell
[All India 2018] protected by thick coating. It is capable of
or germinating into a new plant when comes in
Write the functions of the following in human female contact with suitable and environment conditions
reproductive system: Ovary, oviduct, uterus and moist surface, e.g., in Rhizopus (bread
How does the embryo get nourishment inside the mould), they are formed inside reproductive,
mother’s body? Explain in brief. bob¬like sacs called sporangia.
Ans : [Delhi 2015]
129. What happens when
a. Functions of Ovary, oviduct, uterus a. Testosterone is released in the male reproductive
Functions of Ovary system.
(i) Production of female hormone, oestrogen and b. Pollen grain falls on the stigma of flower.
progesterone. c. Egg fuses with the sperm cell.
(ii) Production of female gamete / egg /germ cell. d. A Planaria is cut into three different pieces.
Functions of Oviduct: e. Buds are formed on the notches of leaf of the
(i) Transfer of female gamete from the ovary. Bryophyllum.
(ii) Site of fertilization.
Ans : [All India 2014-15]
Functions of Uterus:
(i) Implantation of Zygote/ embryo. a. The male shows masculine features and attains
 fertility/ sperm starts forming in testis. organism. This is known as regeneration. Hydra
b. Pollen tube forms and male gametes are carried and Planaria reproduce through this process.
by it to the ovule.
c. Fertilization occurs and a zygote forms. 132. a. Identify the organisms A, B and the mode of
d. Three new Planaria will form due to regeneration. asexual reproduction exhibited by them.
e. New plantlets will form from these buds helping
the plant to propagate vegetatively.

b. How will an organism be benefitted if it reproduces

through spores?
c. Mention the two asexual methods by which hydra
can reproduce. Explain briefly any one such
method.
Ans : [CBSE 2013]
a. (i) Bryophyllum - vegetative propagation. (ii)
Plasmodium - multiple fission.
b. Spores are covered with thick walls that protect
them until they come into contact with a moist
130. Explain what happens when: surface.
a. Testosterone is released in males. c. Budding and Regeneration.
b. Pollen grain falls on the stigma of the flower. Budding : A bud develops as an outgrowth due to
c. Egg fuses with sperm cell. repeated cell division at a specific site, these buds
d. Planaria is cut into many pieces. develop into tiny individuals, mature and detach
e. Buds are formed on the notches of the Bryophyllum from the parent to become new individuals.
leaf. Regeneration: Specialized cells divide to form
Ans : [CBSE 2014, 2015] large number of cells and undergo changes to
a. (i) Formation of sperms, change in appearance. become various cell types and tissues.
(ii) Thick hair growth on the face and voice begin
133. a. Identify the organisms in figure A, B, C and D.
to crack.
b. A tube grows out of the pollen grain and travel
through the style to reach the ovary.
c. Zygote is formed (fertilization).
d. Each piece grows into a complete organism.
e. Buds may fall on the soil and develop into new
plants.

131. Define the following processes:

a. Fertilization
b. Menstruation
c. Binary fission
d. Vegetative propagation
e. Regeneration
Ans :
a. The fusion of male gamete with female gamete is b. Identify the life process commonly shown in all
known as fertilization. the figures,
b. Menstruation cycle takes place every month when c. How is this life process .advantageous to the
egg is not fertilized. It lasts for about two to eight organisms? Mention any two advantages.
days and during this cycle the lining of uterus Ans :
slowly breaks and comes out through the vagina a. (A) Hydra (B) Rhizopus
as blood and mucus. (C) Bryophyllum (D) Planaria
c. Binary fission is the splitting of nucleus into two b. Asexual mode of reproduction
daughter cells which can take place in any plane. c. (i) Only one individual is required. (ii) Progeny
It can be observed in Amoeba. is identical like parents (iii) Produced in large
d. When vegetative part of a plant like the root, number (Any two)
stem or leaves develops into new plant under
appropriate conditions, it is known as vegetative 134. a.Draw a diagram of the longitudinal section of a
propagation. flower and label on it sepals, petal, ovary and
e. When body of an organism cuts into any number stigma.
of pieces and each piece grows into a complete b. Write the names of male and female parts of a
Chap 8 : How Do Organisms Reproduce

flower.
Ans : [All India 2010, 2015]
a.

b. Male Part : Stamen; Female Part : Carpel/pistil

135. a.Draw a sectional view of human female

reproductive system and label the part where:
(i) Eggs develop
(ii) Fertilization takes place
(iii) Fertilized eggs get implanted.
b. Describe in brief, the changes the uterus undergoes:
(i) To receive the zygote
(ii) If zygote is not formed.
Ans : [Delhi 2008, All India 2014, CBSE 2015]
a.

(i) Ovary
(ii) Oviduct or fallopian tube
(iii) Uterus or uterus wall
b. (i) It becomes thicker due to development of
blood vessels and glands in it.
(ii) It gets peeled and shed off along with mucus,
blood, dead ovum during menstruation