Which of the following compounds can liberate methane when treated with excess of methyl magnesium iodide in dry ether.
(a) `CH_3-CH_2-CH_2OH`
(b) `CH_3-CH_2-C-=CH`
(c) `CH_3-CH_2-COOH`
(d) `CH_3-CH_2-CHO`

Options

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

Explanation

To determine which of the given compounds can liberate methane when treated with excess methyl magnesium iodide (a Grignard reagent) in dry ether, we need to analyze each compound for the presence of acidic hydrogen atoms that can react with the Grignard reagent.

### Step-by-Step Solution:

1. **Understanding Grignard Reagent**:
- The Grignard reagent (RMgX) acts as a strong base and can react with compounds that have acidic hydrogen atoms. The reaction typically involves the Grignard reagent abstracting a proton (H⁺) from an acidic hydrogen, leading to the formation of methane (CH₄) and a corresponding magnesium salt.

2. **Analyzing Each Compound**:
- **(a) `CH₃-CH₂-CH₂OH` (Propan-1-ol)**:
- This compound is an alcohol. The hydroxyl (-OH) group has an acidic hydrogen that can be removed by the Grignard reagent.
- Reaction:
\[ CH₃MgI + CH₃-CH₂-CH₂OH \rightarrow CH₄ + CH₃-CH₂-CH₂O^−MgI^+ \]
- Methane is liberated.

- **(b) `CH₃-CH₂-C≡CH` (1-Butyne)**:
- This compound is a terminal alkyne. The hydrogen atom attached to the terminal carbon is acidic and can also be removed by the Grignard reagent.
- Reaction:
\[ CH₃MgI + CH₃-CH₂-C≡CH \rightarrow CH₄ + CH₃-CH₂-C≡C^−MgI^+ \]
- Methane is liberated.

- **(c) `CH₃-CH₂-COOH` (Propanoic acid)**:
- This compound is a carboxylic acid. The hydrogen atom of the carboxylic group (-COOH) is highly acidic and can be removed by the Grignard reagent.
- Reaction:
\[ CH₃MgI + CH₃-CH₂-COOH \rightarrow CH₄ + CH₃-CH₂-COO^−MgI^+ \]
- Methane is liberated.

- **(d) `CH₃-CH₂-CHO` (Ethanal)**:
- This compound is an aldehyde. The hydrogen attached to the carbonyl carbon is not acidic enough to be removed by the Grignard reagent.
- Therefore, no reaction occurs, and methane is not liberated.

3. **Conclusion**:
- The compounds that can liberate methane when treated with excess methyl magnesium iodide are (a) Propan-1-ol, (b) 1-Butyne, and (c) Propanoic acid. The only compound that does not liberate methane is (d) Ethanal.

### Final Answer:
The compounds that can liberate methane are (a), (b), and (c).