Question

Which of these reactions is not a part of breakdown of ozone in stratosphere?

• A. \(CF_2Cl_2(g)\xrightarrow{uv}\dot{C}l(g)+\dot{C}F_2Cl(g)\)
• B. \(C\dot{l}(g)+O_3(g)\rightarrow Cl\dot{O}(g)+O_2(g)\)
• C. \(Cl\dot{O}(g)+O(g)\rightarrow C\dot{l}(g)+O_2(g)\)
• D. \(2Cl\dot{O}\rightarrow ClO_2(g)+C\dot{l}(g)\)

Hint:

The breakdown of ozone in the stratosphere involves a catalytic cycle where chlorine atoms and chlorine monoxide are continuously regenerated to destroy ozone. Reactions outside this cycle are not part of the process.

Answer 1

The Correct Option is D

Breakdown of Ozone in the Stratosphere: 

The breakdown of ozone in the stratosphere involves the following steps:

1. Initiation: Chlorofluorocarbons (CFCs), such as CF₂Cl₂, are photodissociated by ultraviolet radiation to release chlorine atoms.
   CF₂Cl₂(g) \( \xrightarrow{\text{uv}} \) CF₂Cl(g) + Cl(g)
2. Ozone Destruction (Catalytic Cycle):
   (a) Chlorine atoms react with ozone molecules to produce chlorine monoxide (ClO) and oxygen gas:
   Cl(g) + O₃(g) → ClO(g) + O₂(g)
   (b) Chlorine monoxide reacts with atomic oxygen to regenerate chlorine atoms and produce more oxygen gas:
   ClO(g) + O(g) → Cl(g) + O₂(g)
3. Net Reaction: The overall reaction destroys ozone while regenerating chlorine atoms, allowing the cycle to continue:
   O₃ + O → 2O₂

Analysis of Options:

1. Option (1): This reaction represents the photodissociation of CF₂Cl₂, which is part of the initiation step in ozone breakdown. This is correct.
2. Option (2): This reaction shows chlorine reacting with ozone to form chlorine monoxide and oxygen gas, which is part of the catalytic cycle. This is correct.
3. Option (3): This reaction shows chlorine monoxide reacting with atomic oxygen to regenerate chlorine and produce oxygen gas, which is part of the catalytic cycle. This is correct.
4. Option (4): This reaction suggests that two chlorine monoxide molecules react to form ClO₂ and Cl. This does not occur in the stratosphere and is not part of the catalytic cycle. This is incorrect.

The correct answer is option (3).