Which of the following reaction can be used to prepare methane ?
(a) Clemmensen reduction
(b) Wurtz reaction
(c) Catalytic reduction of methyl iodide
(d) Reduction of methyl iodide by using a zinc- copper couple

Options

A. a, b
B. c, d
C. a, c
D. b, d

Answer

To determine which reactions can be used to prepare methane from the given options, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option (a): Clemmensen Reduction**
- Clemmensen reduction is used to reduce carbonyl compounds (like ketones and aldehydes) to alkanes using zinc amalgam and hydrochloric acid.
- For example, if we take a ketone like acetone (CH3COCH3), the reduction would yield propane (CH3CH2CH3), not methane (CH4).
- **Conclusion:** Clemmensen reduction cannot produce methane.

2. **Option (b): Wurtz Reaction**
- The Wurtz reaction involves the coupling of alkyl halides in the presence of sodium metal to form higher alkanes.
- For example, if we take methyl chloride (CH3Cl) and react it with sodium, we would get ethane (C2H6), not methane.
- **Conclusion:** Wurtz reaction cannot produce methane.

3. **Option (c): Catalytic Reduction of Methyl Iodide**
- The catalytic reduction of methyl iodide (CH3I) can be performed using reducing agents like lithium aluminum hydride (LiAlH4).
- The reaction can be represented as:
\[ \text{CH}_3\text{I} + \text{LiAlH}_4 \rightarrow \text{CH}_4 + \text{LiI} \]
- This reaction produces methane (CH4).
- **Conclusion:** Catalytic reduction of methyl iodide can produce methane.

4. **Option (d): Reduction of Methyl Iodide by Using Zinc-Copper Couple**
- This reaction involves the reduction of methyl iodide (CH3I) using a zinc-copper couple.
- The reaction can be represented as:
\[ \text{CH}_3\text{I} + \text{Zn-Cu} \rightarrow \text{CH}_4 + \text{HI} \]
- This reaction also produces methane (CH4).
- **Conclusion:** Reduction of methyl iodide using a zinc-copper couple can produce methane.

### Final Answer:
The reactions that can be used to prepare methane are:
- (c) Catalytic reduction of methyl iodide
- (d) Reduction of methyl iodide by using a zinc-copper couple

Thus, the correct options are **C and D**.