JEE Main 2023 — Environmental Chemistry Question with Solution

The breakdown of ozone in the stratosphere largely involves a series of reactions often initiated by free radicals, such as chlorine (Cl), bromine (Br), or nitric oxide (NO) radicals. In particular, chlorine atoms, which can come from substances like chlorofluorocarbons (CFCs), can catalyze the destruction of ozone.

The first three reactions listed are all part of the ozone breakdown process:

Option A: This is the photodissociation of a chlorofluorocarbon, which releases a chlorine atom (a free radical) that can participate in ozone destruction.

$$\mathrm{C}{\mathrm{F}}_2\mathrm{C}{\mathrm{l}}_2(\mathrm{g})\stackrel{\mathrm{uv}}{\to }\mathrm{Cl}(\mathrm{g})+\mathrm{C}{\mathrm{F}}_2\mathrm{Cl}(\mathrm{g})$$

Option B: This reaction shows a chlorine atom catalyzing the destruction of ozone, forming ClO and O2.

$$\mathrm{Cl}(\mathrm{g})+{\mathrm{O}}_3(\mathrm{g})\to \mathrm{ClO}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})$$

Option D: This reaction shows a ClO radical reacting with a single oxygen atom to regenerate the Cl radical and form O2. The regenerated Cl radical can then go on to catalyze more ozone destruction, making this a catalytic cycle.

$$\mathrm{ClO}(\mathrm{g})+\mathrm{O}(\mathrm{g})\to \mathrm{Cl}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})$$

However, option C:

$$2ClO\to \mathrm{Cl}{\mathrm{O}}_2+\mathrm{Cl}$$

This reaction is not typically part of the ozone breakdown process. Chlorine monoxide (ClO) radicals generally react with atomic oxygen (O), not with another ClO radical, to regenerate the chlorine radical and produce oxygen (O₂). The product of this reaction, ClO₂, does not commonly appear in the standard ozone depletion mechanisms.