What happens when UV rays act upon CFCs?

The correct answer is Option (3) → Chlorine atoms are set free

Option (1) Fluorine atoms are set free — Incorrect. CFCs contain fluorine, but UV rays release chlorine atoms, not fluorine. The free chlorine breaks down ozone.

Option (2) Carbon atoms get separated — Incorrect. UV rays do not separate carbon atoms from CFCs. They release Cl atoms, which degrade ozone into molecular oxygen.

Option (3) Chlorine atoms are set free — Correct. UV rays act on CFCs in the stratosphere and set free chlorine atoms. Each Cl atom breaks down ozone into oxygen again and again, acting as a catalyst, so the ozone layer thins.

Option (4) Hydrogen atoms get oxidized — Incorrect. The ozone-depleting step is the release of chlorine atoms by UV rays. Oxidation of hydrogen atoms is not part of it.

Note: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Ozone Depletion in the Stratosphere – “… CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts; Cl atoms are not consumed in the reaction.”