Reaction of carbonyl compound with one of the following reagents involves nucleophilic addition followed by elimination of water. The reagent is:

Options

A. Hydrocyanic acid
B. Sodium hydrogen sulphite
C. A Grignard reagent
D. Hydrazine in presence of feebly acidic solution

Answer

To solve the question regarding the reaction of a carbonyl compound with a reagent that involves nucleophilic addition followed by the elimination of water, we can follow these steps:

### Step 1: Identify the Carbonyl Compound
A carbonyl compound has a functional group characterized by a carbon atom double-bonded to an oxygen atom (C=O). This includes aldehydes and ketones.

### Step 2: Understand Nucleophilic Addition
Nucleophilic addition involves a nucleophile attacking the electrophilic carbon atom of the carbonyl group. In our case, we are considering the reaction with hydrazine (NH2-NH2), which acts as a nucleophile.

### Step 3: Reaction with Hydrazine
When hydrazine reacts with a carbonyl compound, the nitrogen in hydrazine attacks the carbonyl carbon, leading to the formation of a tetrahedral intermediate. This intermediate can be represented as follows:

1. The carbonyl compound (R1C=O) reacts with hydrazine (NH2-NH2).
2. The nucleophile (NH2) attacks the carbonyl carbon, resulting in the formation of an intermediate with an -OH group and an -NH2 group attached to the same carbon.

### Step 4: Formation of the Intermediate
The intermediate can be represented as:
- R1C(OH)(NH2)-NH2

### Step 5: Elimination of Water
The next step is the elimination of water (H2O) from the intermediate. This occurs when one of the hydrogen atoms from the -NH2 group and the hydroxyl group (-OH) are removed, resulting in the formation of a double bond between carbon and nitrogen:

- The elimination can be represented as:
- R1C(NH2)=N-H + H2O

### Step 6: Final Product
The final product formed after the elimination of water is called a hydrazone. The structure can be represented as:
- R1C=N-NH2

### Conclusion
Thus, the reagent that facilitates nucleophilic addition followed by the elimination of water is **hydrazine (NH2-NH2)**.