The reaction ,
`CH_(3)CHO + H_(2) N - NH_(2) rarr CH_(3) = N.NH_(2)` is :

Options

A. Elimination
B. Addition
C. Addition-elimination
D. None of the above

Explanation

To solve the question regarding the reaction of acetaldehyde (CH₃CHO) with hydrazine (H₂N-NH₂), we will analyze the reaction step by step.

### Step 1: Identify the Reactants
The reactants in this reaction are:
- Acetaldehyde (CH₃CHO)
- Hydrazine (H₂N-NH₂)

### Step 2: Nucleophilic Attack
The nitrogen atom in hydrazine has a lone pair of electrons and acts as a nucleophile. It attacks the carbon atom of the carbonyl group (C=O) in acetaldehyde. This results in the formation of a tetrahedral intermediate.

**Hint:** Look for the nucleophile in the reaction and identify how it interacts with the carbonyl group.

### Step 3: Formation of Tetrahedral Intermediate
Upon the nucleophilic attack, the oxygen atom of the carbonyl group becomes negatively charged (alkoxide ion), and the nitrogen atom becomes positively charged due to the addition of the hydrazine.

**Hint:** Remember that the carbonyl carbon is electrophilic and will be attacked by the nucleophile.

### Step 4: Proton Transfer
In the tetrahedral intermediate, a proton transfer occurs. The positively charged nitrogen atom (NH₂⁺) loses a proton (H⁺), which stabilizes the intermediate and leads to the formation of a hydroxyl group (–OH) on the carbon atom.

**Hint:** Consider how charge stabilization occurs through proton transfer in the intermediate.

### Step 5: Elimination of Water
Upon heating, the intermediate undergoes dehydration (loss of water). The hydroxyl group (–OH) and a hydrogen atom (H) from the nitrogen lead to the formation of a double bond between carbon and nitrogen, resulting in the formation of a hydrazone.

**Hint:** Dehydration reactions often lead to the formation of double bonds; keep an eye on the groups that are eliminated.

### Step 6: Final Product
The final product of the reaction is a hydrazone, specifically CH₃=N-NH₂. This compound is formed after the elimination of water from the tetrahedral intermediate.

**Hint:** Identify the final structure and ensure that it matches the expected product of the reaction.

### Conclusion
The reaction of acetaldehyde with hydrazine is characterized by the following steps: nucleophilic attack, formation of a tetrahedral intermediate, proton transfer, and elimination of water, leading to the formation of a hydrazone. This reaction is classified as an addition-elimination reaction.

### Final Answer
The reaction is an **addition-elimination reaction**.