* Salt water is a mixture. It's composed of the compound sodium chloride (NaCl) dissolved in water (H₂O).

* Oxygen (O₂) is an element. It's a pure substance that cannot be broken down further by chemical means.

* Air is a mixture. It's primarily composed of nitrogen (N₂), oxygen (O₂), and other gases in smaller amounts.

Therefore, neither salt water nor air is an element.