Chlorination of methane does not occur in dark because

Options

A. methane can form free radicals in presence of sunlight only
B. to get chlorine free radicals from `Cl_2` molecules energy is required. It cannot happen in dark
C. substitution reaction can take place only in sunlight and not in dark
D. termination step cannot take place in dark . It requires sunlight

Answer

To answer the question "Chlorination of methane does not occur in dark because...", we need to analyze the chlorination process of methane step by step.

### Step-by-Step Solution:

1. **Understanding Chlorination of Methane**:
- The chlorination of methane (CH₄) involves a reaction with chlorine gas (Cl₂) to form chloromethane (CH₃Cl) and hydrogen chloride (HCl). This reaction occurs through a free radical mechanism.

2. **Chain Initiation Step**:
- The first step in the chlorination process is called the chain initiation step. This step requires energy to break the Cl-Cl bond in chlorine molecules (Cl₂) to form chlorine free radicals (Cl•).
- This energy is provided by ultraviolet (UV) light. In the absence of light, the bond between chlorine atoms cannot break, and thus, chlorine free radicals cannot be formed.

3. **Chain Propagation Step**:
- Once the chlorine free radicals are formed, they can react with methane. The chlorine free radical (Cl•) abstracts a hydrogen atom from methane, forming a methyl radical (CH₃•) and hydrochloric acid (HCl).
- The methyl radical can then react with another chlorine molecule to produce chloromethane (CH₃Cl) and regenerate another chlorine free radical.

4. **Termination Step**:
- The termination step involves the combination of free radicals to form stable products. This step can occur once the free radicals are present.
- However, without the initiation step occurring (due to lack of light), the termination step cannot take place.

5. **Conclusion**:
- Therefore, chlorination of methane does not occur in the dark because the chain initiation step, which is essential for the formation of chlorine free radicals, requires light. Without light, the necessary energy to break the Cl-Cl bond is not available, preventing the reaction from proceeding.

### Final Answer:
Chlorination of methane does not occur in the dark because the initiation of the reaction requires light to produce chlorine free radicals, which is essential for the reaction to proceed.