CSIR NET June 2016 Q69: Meteorology
The Antarctic ozone hole forms through heterogeneous chemistry on polar stratospheric cloud (PSC) surfaces that activates chlorine from CFCs, with catalytic ozone destruction requiring returning sunlight in spring.
During the dark polar winter, PSCs form in the extremely cold stratosphere and provide surfaces for reactions converting stable chlorine reservoir species from CFCs into reactive chlorine (e.g., Cl2, ClO). When sunlight returns in spring, UV photolyzes these reactive species, releasing Cl radicals that catalytically destroy ozone. All three factors -- PSCs, CFCs, and sunlight -- must combine for the ozone hole to form. Option 4 is correct.
1) Tropospheric clouds play no role in stratospheric ozone chemistry. 2) H2O and CO2, while present, are not the key reactive chlorine sources; CFCs are essential and missing here. 3) CFCs are correct but H2O/CO2 are not the other two required factors — PSCs and sunlight are. 4) Correct — matches the well-established mechanism (PSCs + CFCs + sunlight).