Question

which of the following is not an air pollutant? oxygen carbon monoxide sulfur oxides ozone

Explanation:

Air pollutants are substances that harm air quality. Oxygen ($O_2$) is essential for life and a natural component of clean air, not a pollutant. Carbon monoxide (CO) is toxic, sulfur oxides (e.g., $SO_2$) cause acid rain, and ground - level ozone (from pollution reactions) is harmful. So oxygen is not an air pollutant.

Answer:

A. oxygen