`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 problem, we will analyze the given reactions step by step, identifying the functional groups in compounds A, B, C, and D.

### Step 1: Identify Compound A
- **Starting Compound (A)**: The question indicates that the reaction starts with a compound that undergoes reduction with Sn and HCl.
- **Functional Group in A**: The starting compound is **Nitrobenzene (C6H5NO2)**, which contains the **Nitro group (–NO2)**.

### Step 2: Identify Compound B
- **Reaction with Sn/HCl**: Nitrobenzene is reduced to form Aniline.
- **Functional Group in B**: The product of this reaction is **Aniline (C6H5NH2)**, which contains the **Amino group (–NH2)**.

### Step 3: Identify Compound C
- **Reaction with NaNO2 and HCl**: Aniline reacts with sodium nitrite (NaNO2) in the presence of hydrochloric acid (HCl) to form a diazonium salt.
- **Functional Group in C**: The product formed is **Benzene Diazonium Chloride (C6H5N2Cl)**, which contains the **Diazonium group (–N2+Cl)**.

### Step 4: Identify Compound D
- **Reaction with HOH (Water)**: The diazonium salt reacts with water, leading to the substitution of the diazonium group with a hydroxyl group.
- **Functional Group in D**: The product of this reaction is **Phenol (C6H5OH)**, which contains the **Hydroxyl group (–OH)**.

### Step 5: Final Reduction to Benzene
- **Reduction with Zn dust**: The phenol undergoes reduction with zinc dust to yield benzene.
- **Final Product**: The final product is **Benzene (C6H6)**.

### Summary of Functional Groups
- **Compound A**: Nitro group (–NO2)
- **Compound B**: Amino group (–NH2)
- **Compound C**: Diazonium group (–N2+Cl)
- **Compound D**: Hydroxyl group (–OH)

### Final Answer
- A: Nitro group (–NO2)
- B: Amino group (–NH2)
- C: Diazonium group (–N2+Cl)
- D: Hydroxyl group (–OH)