Q. Which of the following are secondary pollutants?

1. Ozone
2. Sulphur dioxide
3. Nitrogen oxides
4. Carbon monoxide

Select the correct option from the codes given below:
Answer: 1 only
Notes: Ozone (O3) is a secondary pollutant formed by photochemical reactions involving primary pollutants such as nitrogen oxides (NOx) and volatile organic compounds. Sulphur dioxide (SO2), nitrogen oxides (NOx), and carbon monoxide (CO) are primarily emitted directly into the atmosphere from combustion and industrial processes. Thus, only ozone is a secondary pollutant among the options given.