Which can not be prepared by Kolbe’s electrolytic reaction using single salt -

Options

A. `CH_(4)`
B. `C_(2)H_(6)`
C. `C_(4)H_(10)`
D. `H_(2)`

Answer

To solve the question "Which can not be prepared by Kolbe’s electrolytic reaction using a single salt?", we need to understand the Kolbe electrolysis process and its limitations.

### Step-by-Step Solution:

1. **Understanding Kolbe Electrolysis**:
- Kolbe electrolysis is a method used to produce alkanes from carboxylic acids through the process of electrolysis. In this reaction, carboxylate ions (from carboxylic acids) are oxidized at the anode to form free radicals, which then couple to form alkanes.

2. **Reaction Mechanism**:
- When two moles of a carboxylic acid (e.g., acetic acid, CH3COOH) are electrolyzed, they form carboxylate anions (CH3COO⁻).
- These anions lose electrons to form free radicals (CH3COO•).
- The free radicals then undergo decarboxylation, releasing CO2 and forming alkyl free radicals (e.g., CH3•).
- Finally, these alkyl radicals combine to form alkanes (e.g., C2H6 from two CH3• radicals).

3. **Analyzing Possible Products**:
- The Kolbe electrolysis can yield various alkanes depending on the starting carboxylic acid.
- For example, using acetic acid (CH3COOH) can yield ethane (C2H6), and using propanoic acid (CH3CH2COOH) can yield butane (C4H10).

4. **Identifying Limitations**:
- The Kolbe electrolysis requires at least two carbon atoms to form a stable alkane. Therefore, it cannot produce methane (CH4) from a single salt (like sodium acetate) since it would require a carboxylic acid with only one carbon atom, which is not feasible in this process.

5. **Conclusion**:
- The product that cannot be prepared by Kolbe’s electrolytic reaction using a single salt is **methane (CH4)**.

### Final Answer:
Methane (CH4) cannot be prepared by Kolbe’s electrolytic reaction using a single salt.