In the following reaction sequences,
`Cl-Cl rarr overset(.)Cl+overset(.)Cl" …(1)"`
`overset(.)Cl+CH_(4)rarroverset(.)CH_(3)+HCl" …..(2)"`
`overset(.)CH_(3)+overset(.)Cl_(2)rarrCH_(3)Cl+overset(.)Cl" ....(3)"`
`overset(.)CH_(3)+overset(.)CH_(3)rarrCH_(3)-CH_(3)" ....(4)"`
the termination step is

Options

A. reaction 1
B. reaction 2
C. reaction 3
D. reaction 4

Answer

To determine the termination step in the given reaction sequences, we need to analyze each step of the radical chain reaction. Here’s a step-by-step breakdown:

### Step 1: Identify the Reaction Steps
1. **Step 1:** \( \text{Cl-Cl} \rightarrow \overset{\cdot}{\text{Cl}} + \overset{\cdot}{\text{Cl}} \) (Initiation)
- This step involves the homolytic cleavage of the Cl-Cl bond, producing two chlorine radicals.

2. **Step 2:** \( \overset{\cdot}{\text{Cl}} + \text{CH}_4 \rightarrow \overset{\cdot}{\text{CH}}_3 + \text{HCl} \) (Propagation)
- Here, the chlorine radical abstracts a hydrogen atom from methane, forming a methyl radical and hydrochloric acid.

3. **Step 3:** \( \overset{\cdot}{\text{CH}}_3 + \overset{\cdot}{\text{Cl}}_2 \rightarrow \text{CH}_3\text{Cl} + \overset{\cdot}{\text{Cl}} \) (Propagation)
- The methyl radical reacts with chlorine gas, leading to the formation of chloromethane and regenerating a chlorine radical.

4. **Step 4:** \( \overset{\cdot}{\text{CH}}_3 + \overset{\cdot}{\text{CH}}_3 \rightarrow \text{CH}_3\text{-CH}_3 \) (Termination)
- In this step, two methyl radicals combine to form ethane, a stable molecule without any radicals.

### Step 2: Identify the Termination Step
- The termination step is characterized by the combination of two radical species to form a stable product. In this case, the fourth reaction, where two methyl radicals combine to form ethane, is the termination step.

### Conclusion
The termination step in the given reaction sequences is **Step 4**: \( \overset{\cdot}{\text{CH}}_3 + \overset{\cdot}{\text{CH}}_3 \rightarrow \text{CH}_3\text{-CH}_3 \).

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