Here's why:

* Homogeneous Mixture: A mixture where the components are evenly distributed throughout and have a uniform composition.

* Heterogeneous Mixture: A mixture where the components are not evenly distributed and have a non-uniform composition.

Air is composed of various gases like nitrogen, oxygen, carbon dioxide, and others. These gases are evenly distributed throughout the air, and you cannot visually distinguish them from each other. This makes it a homogeneous mixture.