Which is the gas that causes eye irritation as a result of photochemical smog?

Acrolein

The correct answer is option 4. Acrolein.

Acrolein is a colorless, clear liquid with a pungent, suffocating odor. It is a poisonous gas that, if inhaled, can cause serious irritations of the skin, eyes, and respiratory tract. At room temperature, acrolein creates hazardous quantities and is extremely combustible.