What is 'X' in the following reaction ?
`C_(6)H_(5)-C-=C-H overset(Hg^(+2))underset("dil. "H_(2)SO_(4))rarr X`

Options

A. `C_(6)H_(3)-COCH_(3)`
B. `C_(6)H_(5)-CH_(2)CHO`
C. `C_(6)H_(5)-CHO`
D. `C_(6)H_(5)-CH_(2)OH`

Explanation

To determine 'X' in the reaction:

\[ C_6H_5-C \equiv C-H \overset{Hg^{+2}}{\underset{dil. H_2SO_4}{\rightarrow}} X \]

we can follow these steps:

### Step 1: Identify the Reactants
The reactant is phenylacetylene, which is represented as \( C_6H_5-C \equiv C-H \). This compound is an alkyne with a phenyl group attached to one end.

### Step 2: Understand the Role of Mercury(II) Ions
When phenylacetylene reacts with mercury(II) ions (\( Hg^{+2} \)), it forms a mercuric ion complex. The alkyne is electron-rich and will coordinate with the \( Hg^{+2} \) ion, leading to the formation of a non-classical carbocation.

### Step 3: Formation of the Carbocation
The reaction proceeds with the formation of a carbocation where the \( Hg^{+2} \) ion is attached to one of the carbon atoms of the triple bond. The structure can be represented as:

\[ C_6H_5-C^+(Hg^{+2})-C \]

### Step 4: Addition of Water
In the presence of dilute sulfuric acid (\( H_2SO_4 \)), water will attack the more substituted carbon of the carbocation. This is due to Markovnikov's rule, which states that in the addition of HX to alkenes, the more substituted carbon will receive the electrophile.

### Step 5: Formation of the Alcohol
The water molecule adds to the more substituted carbon, leading to the formation of an alcohol. The structure will be:

\[ C_6H_5-C(OH)-C(Hg^{+}) \]

After the addition, the \( Hg^{+} \) will be replaced by a proton, leading to the formation of an enol.

### Step 6: Tautomerization
The enol form will undergo tautomerization to form the corresponding ketone. The enol structure can be represented as:

\[ C_6H_5-C(OH)=C(H) \]

This will rearrange to the keto form, which is a more stable structure:

### Step 7: Final Product
The final product \( X \) will be:

\[ C_6H_5-C(=O)-C(H)-H \]

This can be simplified to:

\[ C_6H_5-CO-CH_3 \]

### Conclusion
Thus, the final product \( X \) is:

\[ C_6H_5-CO-CH_3 \]