Here's why:

* Air is a mixture: Air is a mixture of gases, primarily nitrogen (about 78%) and oxygen (about 21%). It also contains small amounts of other gases like argon, carbon dioxide, and neon.

* Carbon dioxide is a single compound: Carbon dioxide is a chemical compound made up of one carbon atom and two oxygen atoms (CO2).

* Different properties: Air and carbon dioxide have different physical and chemical properties, such as density, solubility, and reactivity.

While carbon dioxide is a component of air, it makes up only a small percentage of the total air composition. Air is what we breathe to survive, while carbon dioxide is a greenhouse gas that contributes to climate change.