Page 77 - Viva ICSE Science 4 : E-book

Composition of Air

Air is composed of mixture of gases present in the earth’s atmosphere. It mainly consists
of nitrogen and oxygen. It also contains carbon dioxide, argon and other gases in small

quantities. Nitrogen is the most abundant gas present in the air, followed by oxygen.
Oxygen is needed by animals and humans to breathe and survive. It is also necessary for
burning. Carbon dioxide is utilised by plants to carry out photosynthesis.

Water vapour is the invisible and gaseous state of water present
Did You Know!
in the atmosphere. It is one of the important components of air
Nitrogen present in
as it determines the weather of a place. The condensation of the air is necessary
water vapour to its liquid or solid state is responsible for clouds, for the growth of
plants.
rain and snow.

Besides these, air also contains germs, smoke and dust particles in it.

Properties of Air

We already know that air is colourless and odourless. Let’s discuss some more properties

of air.

• Air occupies space

This property can be easily observed when we blow air
in a fl at balloon. It infl ates and becomes big in size. This is
because air occupies the space available inside the balloon

and gives it a shape. Similarly, when air is blown into a fl at
tyre, swimming tube and football, they become infl ated and
change their shape.

• Air has weight

This can be easily observed by comparing the weights of an infl ated object and a
defl ated object. For example, a balloon with air in it is always heavier than a balloon

without air. This is because air has weight and thus, it makes the infl ated object
heavier.

• Air expands on heating

When air gets heated up, the air particles spread out and start moving faster in all
directions. In this way, air expands and fi lls a larger space.

• Air supports burning

Oxygen present in the air helps in burning.

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