Why is air a mixture and not a compound give 4 point to justify your answers?

I'll not give you a whole answer - as this is obviously a homework question !... However - a compound - is the joining of two or more elements to form one molecule. For example - common table salt is a compound of sodium and chlorine. The chemical name for salt is Sodium Chloride. Pure air, however is composed of individual elements (oxygen, nitrogen, hydrogen, argon, carbon and other 'trace' elements) which are 'free-flowing' - in that the individual atoms are not combined into a single atom of air.