Question

Among the following compounds, which one is not primarily responsible for depletion of ozone layer in stratosphere?

• A. \( \text{NO} \)
• B. \( \text{CF}_2\text{Cl}_2 \)
• C. \( \text{CH}_4 \)
• D. \( \text{Cl}_2 \)

Hint:

Methane is primarily associated with Global Warming. CFCs are primarily associated with Ozone Depletion.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Ozone depletion is driven by radical chain reactions in the stratosphere. We identify the substances that act as sources of these radicals or as catalysts for ozone destruction versus those that might act as sinks or have a lesser primary role.
Step 2: Analysis of Compounds:
(A) \( \text{NO} \) (Nitric Oxide): Acts as a catalyst in ozone depletion (\( \text{NO} + \text{O}_3 \to \text{NO}_2 + \text{O}_2 \)). (B) \( \text{CF}_2\text{Cl}_2 \) (CFC-12): A major source of chlorine radicals (\( \text{Cl}^\bullet \)) which destroys ozone. (D) \( \text{Cl}_2 \): Can photodissociate to yield chlorine radicals, directly contributing to depletion. (C) \( \text{CH}_4 \) (Methane): While it is a greenhouse gas, its role in stratospheric chemistry is often to remove chlorine radicals by reacting with them to form HCl (\( \text{CH}_4 + \text{Cl}^\bullet \to \text{CH}_3^\bullet + \text{HCl} \)). This effectively locks up the destructive chlorine in a reservoir species, temporarily mitigating depletion. Thus, it is not primarily responsible for the *depletion* mechanism itself compared to the others.
Step 3: Conclusion:
Methane is less responsible for depletion than NO, CFCs, and Chlorine gas.
Step 4: Final Answer:
\( \text{CH}_4 \) is the correct answer.