Which of the following is a catalytically inactive (or reservoir) molecule containing chlorine in the stratosphere?

Correct option is C

The correct answer is (c) ClONO₂ (Chlorine Nitrate). In the stratosphere, ClONO₂ acts as a reservoir molecule that temporarily holds chlorine in a stable, inactive form. This means chlorine is not free to participate in catalytic ozone destruction while bound in this molecule.
Reservoir species like ClONO₂ can be converted back into active chlorine species under certain conditions (e.g., on the surface of polar stratospheric clouds).
Explanation of Other Options:
· (a) HOCl (Hypochlorous Acid): Although relatively stable, it can photolyze to release active chlorine.
· (b) ClO (Chlorine Monoxide): This is an active chlorine species involved directly in ozone destruction.
· (d) Cl₂ (Chlorine Gas): Can dissociate under UV radiation to release chlorine radicals, making it an active species.
Information Booster: 1. Reservoir Molecules: Compounds like ClONO₂ and HCl temporarily store chlorine and prevent it from destroying ozone.
2. Active Chlorine: Molecules like Cl, ClO, and HOCl participate directly in catalytic ozone depletion.
3. Ozone Depletion: Chlorine radicals catalyze the breakdown of ozone (O₃) into oxygen (O₂).
4. Polar Stratospheric Clouds (PSCs): Facilitate the conversion of reservoir species to active chlorine during polar winters, contributing to ozone depletion.
5. Catalytic Cycle: One chlorine radical can destroy thousands of ozone molecules through catalytic cycles.
Additional Knowledge: · ClONO₂ (Chlorine Nitrate): Forms through the reaction of ClO with NO₂ and is stable under normal conditions.
· HOCl: Can photodissociate to produce Cl and OH radicals.
· ClO: Reacts with ozone in a key step of the ozone destruction cycle.
· Cl₂: Can be converted to Cl radicals under UV light, making it active.