Air is the mixture of different gases . in Air different gases is present hydrogen , nitrogen , carbon dioxide and etc.....

From air earth make up a surface of gravity.... 78 percent of air contain a nitrogen which we breathe... and 21 percent of air contain oxygen and 0.03 percent contain carbon dioxide.

 in air also present water molecules ...in air also present dust particles and pollen grain of flower...

Air pressure become changes place to place .. Air is very necessary for us... 

fresh air is very healthy for us in specially in morning time .... In winter when cold air blows it's very  nice ....