solution, which is a homogeneous mixture
Because there is more than just one thing in it. There is oxygen, nitrogen, carbon dioxide and much more, but none of the elements are chemically combined. If you had the right tools you could...
air is a mixture of several gases: N2 78.5%, O2 21%, CO2 .3% and several gases in trace ammount
Roughly 80% Nitrogen (N)Roughly 20% Oxygen (O)Roughly 0.03% Carbon Dioxide (CO2)Roughly 0.01% Noble Gases, Mainly Argon (Ar)
air is a mixture because the elements of air are not chemically bonded but are the same like O2,No2.