Sodium salt of the following acid which is needed for the preparation of methane:

Options

A. Ethanoic acid
B. Propanoic acid
C. Butanoic acid
D. Pentanoic acid

Explanation

To determine the sodium salt of the acid needed for the preparation of methane, we can follow these steps:

### Step 1: Understand the target compound
Methane is the simplest hydrocarbon, represented by the chemical formula CH₄.

### Step 2: Identify the method of preparation
Methane can be prepared from carboxylic acids through a process known as decarboxylation. This involves the use of the sodium salt of a carboxylic acid and heating it with soda lime (a mixture of sodium hydroxide and calcium oxide).

### Step 3: Write the general reaction
The general reaction for the decarboxylation of a sodium salt of a carboxylic acid can be represented as:
\[ \text{RCOO}^- \text{Na}^+ + \text{NaOH} + \text{CaO} \rightarrow \text{R-H} + \text{Na}_2\text{CO}_3 \]
Where R represents the alkyl group derived from the carboxylic acid.

### Step 4: Identify the appropriate acid
To produce methane (CH₄), we need to find a carboxylic acid that, when decarboxylated, will yield a one-carbon alkyl group (methyl group, CH₃). The sodium salt of acetic acid (ethanoic acid) is CH₃COO⁻Na⁺.

### Step 5: Perform the reaction
When the sodium salt of acetic acid is heated with soda lime, the reaction proceeds as follows:
\[ \text{CH}_3\text{COO}^- \text{Na}^+ + \text{NaOH} + \text{CaO} \rightarrow \text{CH}_4 + \text{Na}_2\text{CO}_3 \]
This reaction produces methane (CH₄) and sodium carbonate (Na₂CO₃).

### Conclusion
Thus, the sodium salt of the acid needed for the preparation of methane is the sodium salt of acetic acid (ethanoic acid).

### Final Answer
The sodium salt of acetic acid (ethanoic acid) is needed for the preparation of methane.

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