What is X in the following sequence of reaction?
`X underset(1//2H_2)overset(Na)to Z overset(NaOH// CaO) to CH_4 uarr`

Options

A. Methane
B. Ethanolc acid
C. Propane
D. None of these

Explanation

To determine what X is in the given sequence of reactions, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction Sequence**:
The reaction sequence provided is:
\[ X \xrightarrow{(1/2)H_2, Na} Z \xrightarrow{NaOH, CaO} CH_4 \]
Here, we need to identify what X is, given that it eventually leads to methane (CH₄).

2. **Analyzing the First Reaction**:
The first part of the reaction indicates that X reacts with sodium (Na) and half a molecule of hydrogen (1/2 H₂). This suggests a reduction reaction, where X is likely a carboxylic acid or a similar compound that can be converted into a sodium salt.

3. **Identifying Possible Candidates for X**:
The options provided are:
- Methane (CH₄)
- Ethynoic acid (CH₃COOH)
- Propane (C₃H₈)
- Nonanes (C₉H₂₀)

Among these, ethynoic acid (CH₃COOH) stands out as a suitable candidate because it can react with sodium and hydrogen to form a sodium salt.

4. **Formation of Z**:
When ethynoic acid (CH₃COOH) reacts with sodium and hydrogen, it forms sodium ethanoate (CH₃COONa). This compound is our Z.

5. **Analyzing the Second Reaction**:
The next part of the reaction shows that Z (sodium ethanoate) reacts with sodium hydroxide (NaOH) and calcium oxide (CaO). This reaction typically leads to the decarboxylation of the sodium salt, producing methane (CH₄) and sodium carbonate (Na₂CO₃).

6. **Conclusion**:
Since the sequence of reactions starting from X leads to the formation of methane (CH₄) through the intermediate Z, we conclude that X must be ethynoic acid (CH₃COOH).

Thus, the answer is:
\[ \text{X is } \text{ethynoic acid (CH}_3\text{COOH)}. \]