Q1. What is the composition of air?

Answer: Air is the composition of nitrogen(78.09%), oxygen(20.95%), argon(0.93), carbon dioxide(0.04%), dust, smoke and variable amount of water vapour.

Q2. Which gas in the atmosphere is essential for respiration?

Answer: Oxygen present in the atmosphere is essential for respiration.

Q3. How will you prove that air supports burning?

Answer: We can prove that air supports burning with the following experiment:

👉Take a burning candle in a tub filled by some water. After that cover that candle with an inverted glass.

👉We will observe that the candle extinguished after burning for some time, and the water level inside the inverted glass will rise up. This will happen because the component of oxygen which was helping in burning the candle was used up and thus water occupies that space.

Q4. How will you show that air is dissolved in water?

Answer: Air is dissolved in water can be shown by the following experiment:

👉Take some water in a beaker and heat it slowly. After some-time, we can observe tiny bubbles rising upward from the inner surface of the water. Therefore, this shows that after heating the water, air dissolved in water escapes in the form of these bubbles.

Q5. Why does a lump of cotton wool shrink in water?

Answer: A lump of cotton wool shrinks in water because the air present between the fibres of the cotton lump is replaced by water that makes the cotton fibres heavy and the layers to be stuck together.

Q6. The layer of air around the earth is known as ______________.

Answer: atmosphere.

Q7. The component of air used by green plants to make their food, is ______________.

Answer: carbon dioxide

Q8. List five activities that are possible due to the presence of air.

Answer: Five activities that are possible due to presence of air:

(i) Respiration

(ii) Photosynthesis

(iii) Burning of substance.

(iv) Formation of cloud.

(v) Winnowing (method of separation)

Q9. How do plants and animals help each other in the exchange of gases in the atmosphere?

Answer: Both plants and animals depend on each other or help each other in the exchange of gasses in the atmosphere as follows:

👉Plants need carbon dioxide for the preparation of their food by the process of photosynthesis and thus they release oxygen.

👉Animals take oxygen for respiration and give out carbon dioxide.