In the following reactions, reactants A, B and C are:
`C_2H_5NH_2 + A to C_2H_5N = CN - C_6H_5 + H_2O`
`"Urea" + B to H_2N - NHCONH_2 + NH_3`
`C_2H_5 NH_2 + C to C_2H_5Cl+H_2O+N_2`

Options

A. `CH_3CHO,NH_2 - NH_2 and PCl_5`
B. `C_6H_5CHO,NH_2-NH_2and SOCl_2`
C. `C_6H_5CHO,NH_2-NH_2and NOCl`
D. `CH_3CHO,NH_2-NH_2 and PCl_3`

Answer

To solve the problem, we need to identify the reactants A, B, and C in the given reactions. Let's analyze each reaction step by step.

### Step 1: Analyzing the First Reaction
The first reaction is:
\[ C_2H_5NH_2 + A \rightarrow C_2H_5N = C - C_6H_5 + H_2O \]

1. The reactant \( C_2H_5NH_2 \) is ethylamine.
2. The product \( C_2H_5N = C - C_6H_5 \) suggests that a carbonyl compound is involved, as a water molecule is eliminated (indicating a condensation reaction).
3. The product \( C_6H_5 \) indicates that a phenyl group is involved.
4. The likely structure for \( A \) is benzaldehyde (\( C_6H_5CHO \)), which can react with ethylamine to form an imine and release water.

**Conclusion for A:**
\[ A = C_6H_5CHO \] (Benzaldehyde)

### Step 2: Analyzing the Second Reaction
The second reaction is:
\[ \text{"Urea"} + B \rightarrow H_2N - NHCONH_2 + NH_3 \]

1. Urea is \( NH_2CONH_2 \).
2. The product suggests that \( B \) is a compound that can lead to the formation of another amine and ammonia.
3. The reaction indicates that \( B \) is likely hydrazine (\( NH_2NH_2 \)), which can react with urea to form a compound containing two amine groups and release ammonia.

**Conclusion for B:**
\[ B = NH_2NH_2 \] (Hydrazine)

### Step 3: Analyzing the Third Reaction
The third reaction is:
\[ C_2H_5NH_2 + C \rightarrow C_2H_5Cl + H_2O + N_2 \]

1. The reactant \( C_2H_5NH_2 \) is again ethylamine.
2. The products suggest that a chlorinating agent is involved, as \( C_2H_5Cl \) is produced along with water and nitrogen gas.
3. The likely candidate for \( C \) is sodium nitrite (\( NaNO_2 \)) or nitrosyl chloride (\( NOCl \)), which can lead to the formation of a diazonium salt that decomposes to give nitrogen gas.

**Conclusion for C:**
\[ C = NOCl \] (Nitrosyl chloride)

### Final Summary:
- \( A = C_6H_5CHO \) (Benzaldehyde)
- \( B = NH_2NH_2 \) (Hydrazine)
- \( C = NOCl \) (Nitrosyl chloride)

### Answer:
The correct combination of reactants is:
- A: \( C_6H_5CHO \)
- B: \( NH_2NH_2 \)
- C: \( NOCl \)