The product 'C' in the following reaction is: $C_{6}H_{5}NO_{2}\xrightarrow{Fe/HCl} A\xrightarrow[273K]{NaNO_{2}+HCl} B \xrightarrow[\Delta]{H_2O/H+} C$

Question

Accepted Answer

The reaction sequence provided involves the transformation of nitrobenzene into phenol through a series of steps. Let's break down the process to understand why Option 4, phenol, is the correct answer.

1. **Step 1: Reduction of Nitrobenzene to Aniline**
   - The reaction starts with nitrobenzene ($C_{6}H_{5}NO_{2}$) being reduced by iron (Fe) in the presence of hydrochloric acid (HCl). This reduction converts the nitro group (-NO₂) into an amino group (-NH₂), forming aniline ($C_{6}H_{5}NH_{2}$), which is compound A.

2. **Step 2: Formation of Diazonium Salt**
   - Aniline (A) is then treated with sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at 273 K. This reaction forms a diazonium salt, specifically benzene diazonium chloride ($C_{6}H_{5}N_{2}^+Cl^-$), which is compound B.

3. **Step 3: Hydrolysis to Phenol**
   - The diazonium salt (B) undergoes hydrolysis in the presence of water (H₂O) and an acidic medium (H⁺) with heat (Δ). This process replaces the diazonium group with a hydroxyl group (-OH), resulting in the formation of phenol ($C_{6}H_{5}OH$), which is compound C.

**Why Option 4 (Phenol) is Correct:**
- The final product of the reaction sequence is phenol, as the diazonium salt is hydrolyzed to form phenol. This is a well-known reaction in organic chemistry where diazonium salts are converted to phenols through hydrolysis.

**Why the Other Options are Incorrect:**
1. **Aniline (Option 1):** Aniline is an intermediate (compound A) in the reaction sequence, not the final product. It is formed in the first step but is further transformed into a diazonium salt and then into phenol.

2. **Benzene (Option 2):** Benzene is not formed in this reaction sequence. The process involves the conversion of nitrobenzene to phenol, not to benzene.

3. **Nitrobenzene (Option 3):** Nitrobenzene is the starting material, not the final product. The reaction sequence describes its conversion to phenol, not its regeneration.

In conclusion, the correct answer is Option 4, phenol, as it is the final product of the given reaction sequence.