* Elements are pure substances that cannot be broken down into simpler substances by chemical means. Examples include oxygen (O), nitrogen (N), and carbon (C).

* Compounds are formed when two or more elements chemically combine in a fixed ratio. Examples include water (H₂O) and carbon dioxide (CO₂).

* Mixtures are combinations of two or more substances where each substance retains its own chemical identity. The components of a mixture can be separated by physical means.

Air is a mixture because:

* It contains multiple gases like nitrogen, oxygen, carbon dioxide, and others.

* These gases are not chemically bonded together, but rather physically mixed.

* The proportions of these gases can vary depending on location and other factors.

Therefore, air is a mixture, not an element or compound.