`A overset ( Sn // HCI ) to B underset( HCI , 0 ^@ C ) overset( NaNO_2 ) to C overset( HOH ) to D underset( Delta ) overset( Zn " dust ") to C_6 H_6 `, Functional groups in A, B ,C and D respective are :

Options

A. `-NO_2,-NH_2 ,-N -= N ^(+) Cl^- ,-OH`
B. `OH,-NH_2,-N=N -, -NO`
C. `-NO_2,-NH_2 ,-NH-NH-,-OH`
D. `-NO_2 ,-Cl,-ONO ,-OH`

Answer

To solve the given problem, we will follow the sequential reactions step by step, identifying the functional groups in compounds A, B, C, and D.

### Step 1: Identify Compound A
- The reaction starts with a compound that undergoes reduction. The reagent used is Sn (tin) in the presence of HCl.
- The starting compound is likely to be a nitro compound (NO2 group). The most common nitro compound that can be reduced to an amine is nitrobenzene (C6H5NO2).
- Therefore, **Compound A** is **Nitrobenzene (C6H5NO2)**.

### Step 2: Identify Compound B
- When nitrobenzene (Compound A) is treated with Sn and HCl, it gets reduced to an amine.
- The reduction of nitrobenzene yields aniline (C6H5NH2).
- Therefore, **Compound B** is **Aniline (C6H5NH2)**.

### Step 3: Identify Compound C
- The next step involves treating aniline (Compound B) with NaNO2 and HCl at low temperatures (0 to 5 °C).
- This reaction produces a diazonium salt, specifically benzenediazonium chloride (C6H5N2Cl).
- Therefore, **Compound C** is **Benzenediazonium Chloride (C6H5N2Cl)**.

### Step 4: Identify Compound D
- The diazonium salt (Compound C) is then treated with water (H2O), leading to the formation of phenol (C6H5OH) and the release of nitrogen gas (N2).
- Therefore, **Compound D** is **Phenol (C6H5OH)**.

### Summary of Functional Groups:
- **Compound A (C6H5NO2)**: Nitro group (NO2)
- **Compound B (C6H5NH2)**: Amino group (NH2)
- **Compound C (C6H5N2Cl)**: Diazonium group (N2+)
- **Compound D (C6H5OH)**: Hydroxy group (OH)

### Final Answer
- A: Nitrobenzene (C6H5NO2)
- B: Aniline (C6H5NH2)
- C: Benzenediazonium Chloride (C6H5N2Cl)
- D: Phenol (C6H5OH)