Which one of the following chemicals is responsible for the depletion of ozone layer in the atmosphere?

Answer: (a) Chlorofluorocarbons

CFCs break down in UV light in the stratosphere; the chlorine destroys thousands of ozone molecules each.

The idea

A chlorine atom works as a catalyst: it breaks an ozone molecule and comes out of the reaction unchanged, ready to break the next one. That is why a small amount of CFC does so much damage.

CFC reaches the stratosphere → Ultraviolet light frees a chlorine atom → Chlorine + ozone → chlorine monoxide + oxygen → Chlorine monoxide + oxygen atom → chlorine is free again → The cycle repeats thousands of times

Why the others are wrong

(b) N₂O does deplete ozone (it is now the top emitted ozone-depleter), but CFCs are the textbook answer.

(c) SO₂ causes acid rain.

(d) CO₂ is a greenhouse gas; it doesn’t destroy ozone.

The trap

N₂O is a real ozone-depleter, which makes (b) a clever near-miss.

Also know

Mario Molina and Sherwood Rowland proposed this in 1974 and shared the 1995 Nobel Prize in Chemistry with Paul Crutzen. Bromine from halons works the same way and is even more destructive atom for atom.