* Elements: Elements are the simplest forms of matter that cannot be broken down into simpler substances (like oxygen, nitrogen, etc.).

* Compounds: Compounds are formed when two or more elements chemically combine in a fixed ratio (like water, which is H₂O).

* Mixtures: Mixtures consist of two or more substances that are physically combined but not chemically bonded. The components of a mixture retain their individual properties.

Clean air is primarily a mixture of:

* Nitrogen (N₂): The most abundant gas in the atmosphere.

* Oxygen (O₂): Essential for respiration.

* Argon (Ar): A noble gas.

* Carbon Dioxide (CO₂): A greenhouse gas.

* Other gases: Traces of other gases like neon, helium, methane, etc.

These components are not chemically bonded, and their proportions can vary depending on location and conditions. This is what makes clean air a mixture.