Air — Notes & Practice
Class 4 • Environmental Studies
1) What is Air?
Air is a mixture of gases that surrounds the Earth. It is invisible, tasteless and odorless.
- Air contains oxygen, nitrogen, carbon dioxide, water vapour, dust and other gases.
- Air is present everywhere, even though we cannot see it.
- All living things need air to survive.
2) Composition of Air
- Nitrogen: About 78%
- Oxygen: About 21%
- Carbon dioxide: About 0.03%
- Other gases, water vapour, and dust: Small amounts
3) Importance of Air
- Oxygen in air is needed for breathing and burning.
- Plants use carbon dioxide for photosynthesis.
- Air helps in the water cycle and in maintaining weather.
- Air helps birds and airplanes to fly.
- Air helps in carrying sound.
4) Properties of Air
- Air has weight and occupies space.
- Air exerts pressure on everything around us.
- Air can be compressed and expanded.
5) Uses of Air
- For respiration in humans and animals.
- For photosynthesis in plants.
- For burning fuels.
- In windmills to produce electricity.
- To fill tyres, balloons, and playthings.
6) 20 Important Questions & Answers
1) What is air made up of?
Air is made up of nitrogen, oxygen, carbon dioxide, water vapour, and other gases.
2) Which gas in air is used by humans to breathe?
Oxygen.
3) Which gas in air do plants use for photosynthesis?
Carbon dioxide.
4) What percentage of air is nitrogen?
About 78%.
5) What percentage of air is oxygen?
About 21%.
6) Can air be seen?
No, air cannot be seen but we can feel it.
7) Does air have weight?
Yes, air has weight.
8) What is the importance of oxygen in air?
It is essential for breathing and burning.
9) Why is carbon dioxide important?
Plants need carbon dioxide to make food by photosynthesis.
10) What does air exert on everything around us?
Air exerts pressure.
11) How do birds and airplanes fly?
They fly with the help of air.
12) What role does air play in the water cycle?
Air helps in evaporation and formation of clouds.
13) What is the use of air in windmills?
Air (wind) is used to produce electricity in windmills.
14) What happens when there is no oxygen in air?
Living things cannot survive and burning cannot take place.
15) How does air help in sound?
Air carries sound from one place to another.
16) What is air pressure?
The force exerted by air on everything around us.
17) Name two things we fill with air.
Balloons and tyres.
18) Why do mountaineers carry oxygen cylinders?
Because at high altitudes, air has less oxygen.
19) Which gas in air do animals give out while breathing?
Carbon dioxide.
20) Why is air called a mixture?
Because it is made up of many gases like oxygen, nitrogen, carbon dioxide, and others.