SCIENCE 14. Air Around Us WORKBOOK

 Objective type questions

14. Air Around Us 

1. Choose the correct option. 

a) The amount of nitrogen present in the atmosphere is __________. i) 20% ii) 78% 

iii) 16% iv) 0.03% 

ans: 78% 

b) _________________ gas is used in extinguishing fires. 

i) Oxygen ii) Hydrogen 

iii) Carbon dioxide iv) Nitrogen 

ans: Carbon dioxide 

c) _____________ mark the beginning of the oxygen cycle. i) Bacteria ii) Land animals iii) Sea animals iv) Plants 

ans: Plants 

2. Name the following: 

a) The excessive cutting of trees. 

ans: Deforestation 

b) The envelope of air surrounding the earth. 

ans: Atmosphere 

c) The method used for separation of husk from grains using wind. ans: Winnowing 

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3. State whether the following statements are true or false.  

a) Windmills are used to draw water from tube wells. 

ans: True 

b) The amount of water vapour present in the atmosphere is fixed. ans: False 

c) Nitrogen supports combustion. 

ans: False 

4. Assertion-reasoning type questions: 

In following questions, the Assertion and Reason have been put forward. Read the  statements carefully and choose the correct alternative from the following: (A) Both Assertion and Reason are true and the Reason is a correct explanation  of the Assertion. 

(B) Both Assertion and Reason are true but Reason is not a correct explanation  of the Assertion. 

(C) Assertion is true but the Reason is false. 

(D) Both Assertion and Reason are false. 

a) Assertion: The ruler stoops to one side, when one of the balloons tied at  the two ends of a ruler is punctured. 

Reason: Air is invisible. 

ans: (B) Both Assertion and Reason are true but Reason is not a correct  explanation of the Assertion. 

b) Assertion: Use of alternate sources of energy such as wind energy and  solar energy should be encouraged. 

Reason: Alternate sources of energy do not cause air pollution. 

ans: (A) Both Assertion and Reason are true and the Reason is a correct  explanation of the Assertion.

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Theory type questions

5. Define the following: 

a) Oxygen cycle 

ans: The cycle in nature in which the oxygen is consumed for respiration  and is released during the process of photosynthesis is called oxygen  cycle. 

b) Air pollution 

ans: The presence of undesirable substances in the air that cause harmful  effects is known as air pollution. 

6. Answer the following in brief. 

a) What is the significance of hair and mucus present inside the nose of  human beings? 

ans: They prevent the dust particles from entering our lungs. 

b) Which harmful gases are produced by burning of fuels in automobiles and  factories? 

ans: Harmful gases such as carbon monoxide, oxides of nitrogen and  hydrogen sulphide produced by burning of fuels in automobiles and  factories. 

c) Give one use of nitrogen. 

ans: It is used in the manufacture of fertilisers. 

7. Give reasons for the following statements. 

a) It is difficult to breathe at higher altitudes. 

ans: As the layer of air is very thin at higher altitudes. 

b) If a burning candle is covered using a tumbler, it goes off in sometime. ans: Oxygen is necessary for burning. The candle goes off as it uses up all  

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the oxygen present inside the glass. 

Picture based question

8. Observe the given picture and answer the questions that follow.

a) Why do you see bubbles escaping from the bottle? 

ans: The bottle had air which escaped on tilting the bottle in the form of  bubbles. 

b) What can you conclude from the above activity? 

ans: Air occupies space. 

Real life learning 

9. There is a chemical factory in your locality that emits lots of gases into the atmosphere. The harmful effects of this are seen on people living in nearby areas. Suggest any one step that the chemical factory can follow to reduce air pollution. ans: The chemical factory should install long chimneys so that the harmful  gases are released high up in the air and away from humans. 

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Fun based questions

10. Fill in the missing letters appropriately. 

1. The process of formation of water vapour from water by heating. E V A P O R A T I O N 

2. The harmful substances present in the air.  

P O L L U T A N T S 

HOTS 

11. Higher Order Thinking Skills (HOTS) 

What will happen if all plants were to vanish from the surface of the earth? Justify  your answer. 

ans: ∙ As the plants mark the beginning of the oxygen cycle, no plants means no  photosynthesis. 

∙ No photosynthesis means no oxygen for respiration and the very life on  the earth will come to an end. 

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