NCERT 6th Class (CBSE) Science: Air Around Us

Question: What is the composition of air? or Write a short note on the composition of air.

Answer: Air is mixture of nitrogen, oxygen, carbon dioxide, water vapour and a few other gases. Some dust particles may also be present in it.

Air is a mixture of gases, mainly containing nitrogen (about 78% by volume) and oxygen (about 21% by volume). The remaining 1% is made up a gas called argon (about 0.9%), Carbon dioxide (0.03%) and small amounts of other gases. Varying quantities of dust, smoke and water vapour are also presents. The amount of these in the air varies from place to place and from time to time.

Question: Which gas in the atmosphere is essential for respiration?

Answer: Oxygen.

Question: How will you show that air supports burning?

Answer: Take a small burning candle. Cover the burning candle with a glass jar. After few minutes the candle is extinguished. As the supply of air is stopped due to glass jar the burning of candle is also stopped. This experiment proves that air supports burning

Question: How will you show that air is dissolved in water?

Answer: Take some water in a glass vessel or beaker. Heat it slowly on a tripod stand. Before the water begins to boil, look carefully at the inner surface of the vessel. You will see tiny bubbles on the inside. On heating, air dissolved in water escapes in the form of these bubbles.

Question: Why does a lump of cotton wool shrink in water?

Answer: Lump of cotton wool has air among gaps of cotton fibres. When water replaces the air from these gaps, the cotton lump becomes heavy and also shrinks due to removal of air gaps.