Which one of the following groups represents secondary air pollutants?

Q. Which one of the following groups represents secondary air pollutants?

1. Ozone, Formaldehyde, Peroxy-acetyl-nitrate, and Halogen compounds
2. Formaldehyde, Hydrocarbon, Ozone and Photochemical smog
3. Ozone, Acid mist, Formaldehyde and Photochemical smog
4. Formaldehyde, Acid mists, Hydrocarbon and Photochemical smog

Answer: Ozone, Acid mist, Formaldehyde and Photochemical smog