Aldehydes and ketones give addition reaction with

Options

A. Hydrazine
B. Phenyl hydrazine
C. Semicarbazide
D. Hydrogen cyanide

Answer

To solve the question regarding which substances give addition reactions with aldehydes and ketones, we will analyze each option provided.

### Step 1: Identify the nature of aldehydes and ketones
Aldehydes and ketones contain a carbonyl group (C=O), which is polar due to the difference in electronegativity between carbon and oxygen. This polarity makes the carbon atom electrophilic and susceptible to nucleophilic attack.

**Hint:** Aldehydes and ketones have a carbonyl group that makes them reactive towards nucleophiles.

### Step 2: Analyze the options
1. **Hydrogen (H2)**: This is a diatomic molecule and does not act as a nucleophile. It does not participate in addition reactions with aldehydes or ketones.

**Hint:** Consider whether the substance can donate electrons or act as a nucleophile.

2. **Phenylhydrazine (C6H5NHNH2)**: This compound can react with carbonyl compounds to form hydrazones through a condensation reaction, which involves both addition and elimination (removal of water). However, it is not a straightforward addition reaction.

**Hint:** Look for compounds that can add directly to the carbonyl carbon without elimination.

3. **Semi-carbazide (H2N-NH-C(O)NH2)**: Similar to phenylhydrazine, semi-carbazide reacts with carbonyl compounds to form semi-carbazones through a condensation reaction, which also involves elimination.

**Hint:** Again, focus on whether the reaction is purely an addition reaction.

4. **Hydrogen cyanide (HCN)**: This is a well-known nucleophile. When HCN reacts with aldehydes or ketones, it adds to the carbonyl carbon, forming a cyanohydrin. This is a classic example of a nucleophilic addition reaction.

**Hint:** Identify if the substance can add to the carbonyl carbon without elimination.

### Step 3: Conclusion
Among the given options, only hydrogen cyanide (HCN) is capable of undergoing a straightforward addition reaction with aldehydes and ketones to form cyanohydrins.

Thus, the correct answer is **Hydrogen cyanide (HCN)**.

### Final Answer
**Hydrogen cyanide (HCN) gives addition reactions with aldehydes and ketones.**