* Compound: A substance formed when two or more different elements are chemically combined in a fixed ratio.

* Mixture: A combination of two or more substances where each substance retains its own properties.

CO2 (Carbon Dioxide) is made up of two different elements:

* Carbon (C)

* Oxygen (O)

These elements are chemically bonded in a fixed ratio of one carbon atom to two oxygen atoms. This chemical bonding creates a new substance with properties different from either carbon or oxygen alone.

Therefore, CO2 is a compound.