* Air: Air is a mixture. It's primarily composed of nitrogen and oxygen, but also contains other gases like carbon dioxide, argon, and trace amounts of others.

* Salt: Salt (sodium chloride) is a compound. It's formed by the chemical bonding of sodium and chlorine atoms.

* Water: Water (H₂O) is a compound. It's made up of hydrogen and oxygen atoms chemically bonded together.

* Sulfur: Sulfur is an element. It exists as a pure substance in its elemental form.

In summary: Only air is a mixture. The others are compounds or elements.