Chapter 15: Air Around Us (Solutions)
Posted on : 12-06-2018 Posted by : Admin

Link to Notes on this topic

1. What is the composition of air?

Answer: Air is the mixture of gases like nitrogen, oxygen, carbon dioxide, water vapor and some other gases. Sometimes smoke and dust particles also form the composition of the air depending on the place.

2. Which gas in the air is essential for respiration?

Answer: Oxygen is the gas present in the air which is essential for respiration.

3. How will you prove that air supports burning?

Answer: To prove that air supports burning, put a candle in a tub filled with water. Light the candle and cover it with an inverted glass tumbler. You will find that the candle blows out after burning for some time, and the water level inside the inverted glass rises up to some extent.

As the candle uses oxygen, the space occupied by air inside the glass will decrease. This space is in turn occupied by the water. And thus water enters the glass tumbler. This experiment proves that air supports burning.

4. How will you show that air is dissolved in water?

Answer:To show that air is dissolved in water, take some water in a pan and heat it. Just before water starts to boil, you will notice some bubbles rising on the inner surface of the pan. These bubbles come from the air dissolved in the water. On further heating the water itself turns into vapour and finally begins to boil.

5. Why does a lump of cotton wool shrink in water?

Answer: Air is present in the gaps between the cotton fibers of the lump of cotton wool. When this lump of cotton wool is immersed in water, the air gaps are replaced by water.  Due to this replacement, the cotton becomes heavy and shrinks in water.

6. The layer of air around the earth is known as atmosphere.

7. The component of air used by green plants to make their food is carbon dioxide

8. List five activities that are possible due to presence of air:


(a) Respiration which is vital for the survival of all human beings

(b) Performance of photosynthesis by all green plants

(c) For burning of substances

(d) Movement of sailing yachts, gliders, parachutes, airplanes

(e) Generation of electricity with the help of wind mills

9. How do plants and animals help each other in exchange of gases in the atmosphere?

Answer: It is obvious that animals cannot live without plants. Similarly, plants cannot survive for long without animals. They would consume all the carbon dioxide in the atmosphere. We can see that both need each other, as the balance of oxygen and carbon dioxide in the atmosphere is thus maintained. This shows the interdependence of plants and animals.

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