Theory:

In the olden days, people believed that air is just one single substance. But, experiments conducted by Priestley followed by Ingenhousz and Rutherford have proved that air is a mixture of many gases.
The primary constituent of air is nitrogen, and the second major component is oxygen. Air also contains carbon-di-oxide, water vapour, and dust particles with some other gases like argon, helium, neon, krypton, xenon etc.
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Composition of air
 
This air composition slightly varies from place to place and even from season to season.
 
1. A high amount of carbon-di-oxide can be found in the air over industrial cities than in other open spaces.
 
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Industrial chimneys
 
2. The amount of water vapour is higher in the air of coastal areas than inland areas. Even in rainy seasons, more water vapour (high humidity) is present in the air.
 
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Coastal areas
 
3. Dust quantity is more in windy places than in other areas.
 
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Dusty roads
Nitrogen
Around four-fifths of the atmosphere consists of nitrogen. It occupies around \(78\%\) of our atmosphere. Generally, nitrogen does not support combustion.
 
All living things need nitrogen for their growth. Plants use nitrogen to make proteins which are necessary for their growth. Nitrogen present in the soil acts as a good fertilizer.
 
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Growth of plants