2025 O Level Chem P1 Q40 — Air & Atmosphere / Pollutants Solution

Answer: D. Two pollutants, two different effects.

CFCs: chlorofluorocarbons rise to the stratosphere where UV light splits them into chlorine radicals. These chlorine radicals catalytically destroy ozone (\(\text{O}_3\)) molecules. Effect: decrease the ozone in the upper atmosphere (depleting the ozone layer).

Carbon monoxide (CO): binds tightly to haemoglobin in the blood, preventing oxygen transport. Effect: toxic (poisonous). CO does not cause acid rain — that's \(\text{SO}_2\) and \(\text{NO}_x\).

Only row D combines 'decrease ozone' for CFCs with 'toxic' for CO.