Page 126 - Science Class 6 Times Publication

Observation: After some time, you can see the drops of water on the
outer surface of the glass.

Conclusion: Drops of water on the outer surface of the beaker is due
to the condensation of water vapour present in the air. Formation of
dews on the leaves of plants in the morning is due to the condensation
of water vapour present in air.

Insert gases
Gases like helium, neon, argon, etc are found in the air in less amount.
They do not react with other substances. Therefore, they are called
inert gases. They occupy 0.95% of the total volume of air.

Properties of air

Physical properties of air
a. Air is colourless so that it cannot be seen with naked eyes.
b. Air is a mixture of different gases such as nitrogen, oxygen,
carbon dioxide, inert gases, water vapour, etc.

c. Air has weight.

d. Air ows from one place to another.
e. Air occupies space.

Chemical properties of air
a. Metals like iron get rusted due to reaction of the metal with
oxygen and water vapour present in the air.
b. Various substances like petrol, rewood, diesel, etc burn with

oxygen present in air. Burning means reaction with oxygen.

Main gases of air

Nitrogen, oxygen, carbon dioxide, inert gases, etc are the main gases
present in the air. These gases are important to living things.

Nitrogen

Volume of nitrogen in the air is 78% of total volume of air. It is lighter
gas. Nitrogen is used by plants for the preparation of protein. But
the plants cannot use the atmospheric nitrogen directly. Some plants

Times' Crucial Science and Environment 122 Book 6