Air Around Us
Exercise:
1). What is the composition of air?
Ans: Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour, dust particles and a few other gases.
2). Which gas in the atmosphere is essential for respiration?
Ans: Oxygen in the atmosphere is essential for respiration.
3). How will you prove that air supports burning?
Ans: Fix two small candles of the same length on a table. Light both candles. Cover one of the candles with an inverted glass tumbler. The candle covered with a glass tumbler got extinguished after some time, whereas the other candle continues burning. This experiment shows that air supports burning.
4). How will you show that air is dissolved in water?
Ans: Take some water in a glass or metal container. Heat it slowly on a tripod stand. Well before the water begins to boil, look carefully at the inner surface of the container. You see tiny bubbles on the inside. These bubbles come from the air dissolved in water. When you heat the water, to begin with, the air dissolved in it escapes.
5). Why does a lump of cotton wool shrink in water?
6). The layer of air around the earth is known as the 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 the presence of air.
Ans: The activities that are possible due to presence of air are as follows.
i). breathing of living things
ii). burning of substances
iii). leaves of trees rustle
iv). photosynthesis
v). flying of the kites
9). How do plants and animals help each other in the exchange of gases in the atmosphere?
Ans: The balance of oxygen and carbon dioxide is maintained by the respiration of plants and animals and by photosynthesis in plants.
Additional Questions:
True or false
i). Air occupies space.
Ans: True
ii). Air is present everywhere around us.
Ans: True
iii). Air is transparent.
Ans: True
iv). As we move up in the atmosphere, the air becomes thicker.
Ans: False
v). Air is a mixture of many gases.
Ans: True
vi). Nitrogen supports burning.
Ans: False
vii). Dust particles are always present in air.
Ans: True
Fill in the blanks
i). Air occupies space.
ii). Our earth is surrounded by thin layer of air.
iii). The major part of air is nitrogen.
iv). The presence of water vapour in air is important for the
water cycle in nature.
v). Windmills are used to generate electricity.
Answer the following.
1) Write the properties of air.
Ans: The properties of air are as follows.
i). Air occupies space.
ii). Air is present everywhere around us.
iii). Air is transparent.
2). What is an atmosphere?
Ans: The thin layer of the earth surrounded by air is called as atmosphere.
3). Mention the uses of air.
Ans: The uses of air are as follows.
i). Air helps in the movement of sailing yachts, gliders, parachutes and aeroplanes.
ii). Birds, bats and insects can fly due to the presence of air.
iii). Air also helps in the dispersal of seeds and pollen of flowers of several plants.
iv). Air plays an important role in water cycle.
Name the following
i). important component of air.
Ans: Nitrogen
ii) Two uses of oxygen
Ans: Respiration and burning
iii). source of oxygen in the atmosphere
Ans: photosynthesis by green plants.
iv). percentage of nitrogen in the atmosphere.
Ans: 78.1%
v). percentage of oxygen in the atmosphere.
Ans: 20.9%
Give reason
1). The tilted bottle is filled up with water than the inverted bottle.
Ans: The bottle was filled completely with air even when it turned upside down. That is why the water does not enter the bottle when it is pushed in an inverted position, as there was no space for air to escape. When the bottle was tilted, the air was able to come out in the form of bubbles, and water filled up the empty space that the air has occupied.
2) Mountaineers carry oxygen cylinders with them.
Ans: As we go high in the atmosphere the air becomes rarer. Therefore, to maintain the supply of oxygen the mountaineers carry oxygen cylinders with them.
3). Factories have long chimneys.
Ans: The burning of fuels produces smoke. Smoke contains a few gases and dust particles that are ofter harmful. Long chimneys in factories takes the harmful smoke away from the people. Therefore, factories have long chimneys.
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