`[A] + [B ] to C_2 H_5 NH CONHC_2 H_5 `
`{:( (a ) COCl_2 , (b ) ALCl_3),(( c ) C_2 H_5 NH_2 , (d) CH_2 Br_2 ):}`
here , [A] & [B] are

Options

A. a,b
B. b,c
C. c,d
D. a,c

Answer

To solve the problem, we need to identify compounds [A] and [B] that react to form the product C₂H₅NHCONHC₂H₅. The product is an amide, which suggests that one of the reactants must be an acyl chloride (or similar compound) and the other must be an amine.

### Step-by-Step Solution:

1. **Identify the Product Structure**:
The product C₂H₅NHCONHC₂H₅ indicates that it contains an amide functional group (C=O attached to NH). The structure can be broken down as follows:
- C₂H₅NH- (ethylamine)
- CO (carbonyl group)
- NH (amide linkage)
- C₂H₅ (another ethyl group)

2. **Determine the Reactants**:
To form an amide, we typically need:
- An acyl chloride (which provides the carbonyl group)
- An amine (which provides the nitrogen)

3. **Analyze the Given Options**:
We have four options:
- (a) COCl₂ (which is an acyl chloride)
- (b) AlCl₃ (not relevant for amide formation)
- (c) C₂H₅NH₂ (which is ethylamine)
- (d) CH₂Br₂ (not relevant for amide formation)

4. **Select the Correct Reactants**:
- From the analysis, we can see that:
- [A] = COCl₂ (acyl chloride)
- [B] = C₂H₅NH₂ (ethylamine)

5. **Reaction Mechanism**:
The reaction proceeds as follows:
- The nitrogen in ethylamine (B) acts as a nucleophile and attacks the carbonyl carbon in the acyl chloride (A).
- This results in the formation of an intermediate where the chlorine atom leaves, leading to the formation of the amide C₂H₅NHCONHC₂H₅.

### Conclusion:
Thus, the correct identification of [A] and [B] is:
- [A] = COCl₂
- [B] = C₂H₅NH₂