Which of the following is a mixture?

Explanation:

The correct answer is option D i.e. air is a mixture.

A mixture consists of two or more components mixed in either a definite proportion (homogenous) or indefinite proportion (heterogeneous).

Water (H₂O), oxygen (O₂) and carbon dioxide (CO₂) are all compounds while air is a mixture of various gases, water vapour and other constituents.

Final Answer:

Hence, amongst the following, air is a mixture i.e. option D is the correct answer while the rest are all compounds.