Environmental Issues

Ozone in the stratosphere absorbs harmful ultraviolet radiation, and its depletion is caused mainly by chlorofluorocarbons (CFCs). Once CFCs drift up to the stratosphere, ultraviolet rays act on them to release highly reactive chlorine atoms, which then catalytically degrade ozone into molecular oxygen. Because chlorine acts as a catalyst, a single atom can destroy many ozone molecules without being consumed, which is why CFCs are so damaging. Carbon dioxide is incorrect because it is the principal greenhouse gas linked to global warming, not ozone destruction. Sulphur dioxide contributes to acid rain rather than ozone-layer thinning. Methane is a potent greenhouse gas, again associated with warming rather than catalytic ozone breakdown. As described in NCERT Class 12, Chapter 16 (Environmental Issues), increased UV-B from a thinned ozone layer causes skin ageing, cataracts, and snow-blindness, and the Montreal Protocol was signed to control the emission of ozone-depleting substances. Plausibility check: since only chlorine atoms from CFCs catalytically split ozone, while the other gases act through warming or acidification, the CFC answer is internally consistent.