In the upper atmosphere, the ultra-violet light breaks off a free chlorine atom from chlorofluorocarbon…

Analysis

This question tests your understanding of environmental chemistry, specifically the depletion of the ozone layer by chlorofluorocarbons (CFCs). You need to understand the catalytic role of chlorine atoms in the stratosphere.

Concept Explanation

Chlorofluorocarbons (CFCs) are stable compounds at ground level. However, when they rise into the upper atmosphere (stratosphere), they are exposed to high-energy ultraviolet (UV) radiation. This radiation causes the CFC molecules to undergo photodissociation, which releases a highly reactive free chlorine atom ($Cl\cdot$).

Once released, this chlorine atom acts as a catalyst in a cycle that destroys ozone ($O_3$) molecules. The reaction typically follows this path:

1. $Cl + O_3 \rightarrow ClO + O_2$
2. $ClO + O \rightarrow Cl + O_2$

Because the chlorine atom is regenerated at the end of the cycle, a single chlorine atom can destroy thousands of ozone molecules, leading to the thinning of the ozone layer.

Step-by-Step Solution

1. Identify the trigger: UV light breaks the C-Cl bond in CFCs, creating a free radical chlorine atom.
2. Assess the nature of the atom: Free radicals are atoms or molecules with an unpaired electron, making them extremely chemically reactive.
3. Determine the interaction: Because the chlorine atom is highly reactive, it seeks to stabilize itself by reacting with nearby molecules. In the stratosphere, it encounters ozone ($O_3$) and reacts with it to form chlorine monoxide ($ClO$) and oxygen gas ($O_2$).
4. Evaluate the options: • Option A correctly identifies that the chlorine atom is reactive and targets ozone. • Option B is incorrect because the atom is highly reactive. • Option C is incorrect because the reaction significantly reduces ozone levels. • Option D is incorrect because the process destroys ozone, it does not increase it.

Conclusion

The free chlorine atom is a highly reactive radical that initiates the catalytic destruction of the ozone layer. Therefore, it will attack ozone molecules.

Exam Tip: Whenever you see questions about CFCs and the atmosphere, remember the "Ozone Hole." The key mechanism is that CFCs provide the chlorine, and UV light provides the energy to start the chain reaction that destroys ozone.