For distinction between `CH_(3)CHO` and `C_(6)H_(5)CHO`, the used regent is

Options

A. KCN
B. HCN
C. `NH_(2)OH`
D. `PCl_(5)`

Explanation

To distinguish between acetaldehyde (CH₃CHO) and benzaldehyde (C₆H₅CHO), we can use the reagent potassium cyanide (KCN). Here’s a step-by-step explanation of the process:

### Step 1: Identify the Compounds
- Acetaldehyde (CH₃CHO) is an aliphatic aldehyde.
- Benzaldehyde (C₆H₅CHO) is an aromatic aldehyde.

### Step 2: Choose the Reagent
- The reagent we will use for the distinction is potassium cyanide (KCN).

### Step 3: Reaction with Acetaldehyde
- When acetaldehyde (CH₃CHO) reacts with KCN, it forms a cyanohydrin. The reaction can be represented as follows:

\[ \text{CH}_3\text{CHO} + \text{KCN} \rightarrow \text{CH}_3\text{C(OH)(CN)}\text{K} \]

- The product is a cyanohydrin where the carbonyl group is converted into a hydroxyl group, and a cyanide group is added.

### Step 4: Reaction with Benzaldehyde
- When benzaldehyde (C₆H₅CHO) reacts with KCN, it also forms a cyanohydrin. The reaction can be represented as follows:

\[ \text{C}_6\text{H}_5\text{CHO} + \text{KCN} \rightarrow \text{C}_6\text{H}_5\text{C(OH)(CN)}\text{K} \]

- Similar to acetaldehyde, the carbonyl group in benzaldehyde is converted into a hydroxyl group, and a cyanide group is added.

### Step 5: Analyze the Products
- The key difference lies in the structure of the products:
- The product from acetaldehyde will have a methyl group (CH₃) attached to the carbon bearing the hydroxyl and cyanide groups.
- The product from benzaldehyde will have a phenyl group (C₆H₅) attached to the carbon bearing the hydroxyl and cyanide groups.

### Step 6: Conclusion
- The distinct structures of the cyanohydrin products formed from acetaldehyde and benzaldehyde allow us to differentiate between the two aldehydes. Therefore, the reagent used for this distinction is KCN.

### Final Answer
- The reagent used for the distinction between CH₃CHO (acetaldehyde) and C₆H₅CHO (benzaldehyde) is **KCN**.

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