Question

The gas 'A' is having very low reactivity reaches to stratosphere. It is non-toxic and non-flammable but dissociated by UV-radiations in stratosphere. The intermediates formed initially from the gas 'A' are:

• A. \(\dot{\text{C}}\text{H}_3 + \dot{\text{C}}\text{F}_2\text{Cl}\)
• B. \(\dot{\text{C}}\text{lO} + \dot{\text{C}}\text{H}_3\)
• C. \(\dot{\text{C}}\text{lO} + \dot{\text{C}}\text{F}_2\text{Cl}\)
• D. \(\dot{\text{C}}\text{l} + \dot{\text{C}}\text{F}_2\text{Cl}\)

Hint:

The story of ozone depletion is centered on CFCs. Remember that their stability in the lower atmosphere is why they reach the stratosphere, and the weaker C-Cl bond is the Achilles' heel that releases the ozone-destroying chlorine radical under UV radiation.

Answer 1

The Correct Option is D

To determine which intermediates are formed when the gas 'A' is dissociated by UV radiation in the stratosphere, we must first understand the characteristics and behavior of 'A'. The problem states that 'A' is non-toxic, non-flammable, and susceptible to dissociation by UV radiation.

The description fits chlorofluorocarbons (CFCs), which are compounds containing chlorine, fluorine, and carbon. CFCs are known for their role in ozone depletion because they release chlorine atoms upon exposure to UV radiation in the stratosphere.

Let's identify the intermediates:

1. CFCs, such as CFC-12 (CCl₂F₂), get dissociated by UV radiation. The primary reaction involves the breaking of a carbon-chlorine bond.
2. The UV radiation causes CFCs to release a chlorine radical (Cl˙). The equation for the first step of this decomposition is:
   \(\text{CCl}_2\text{F}_2 \rightarrow \dot{\text{Cl}} + \dot{\text{CF}_2\text{Cl}}\)
3. This shows the formation of two intermediates: a chlorine radical (Cl˙) and a CFC radical (CF₂Cl˙).

Thus, the correct intermediates formed from the dissociation of 'A' by UV radiation are:

\(\dot{\text{Cl}} + \dot{\text{CF}_2\text{Cl}}\)

Explanation for other options:

• \(\dot{\text{C}}\text{H}_3 + \dot{\text{C}}\text{F}_2\text{Cl}\): The presence of a methyl radical (CH₃˙) does not fit the initial decomposition of CFCs.
• \(\dot{\text{C}}\text{lO} + \dot{\text{C}}\text{H}_3\): Formation of ClO radical occurs in a later process when chlorine radicals react with ozone (O₃), not in the initial dissociation.
• \(\dot{\text{C}}\text{lO} + \dot{\text{C}}\text{F}_2\text{Cl}\): Similar to the above, ClO radicals form after reacting with ozone, not immediately during UV dissociation of CFCs.

In conclusion, the correct answer, based on the initial UV-induced breakdown of a typical chlorofluorocarbon, is: \(\dot{\text{Cl}} + \dot{\text{CF}_2\text{Cl}}\).