Aldehydes and ketones may be distinguished by using

Options

A. saturated solution of `NaHSO_3`
B. 2:4 dinitrophenylhydrazine
C. Tollen's reagent
D. Baeyer's reagent

Explanation

To distinguish between aldehydes and ketones, we can use various reagents. Here is a step-by-step solution to the question:

### Step 1: Understand the Properties of Aldehydes and Ketones
Aldehydes and ketones are both carbonyl compounds, but they have different reactivity due to the presence of the carbonyl group (C=O). Aldehydes have at least one hydrogen atom attached to the carbonyl carbon, while ketones have two alkyl groups attached to the carbonyl carbon.

### Step 2: Evaluate the Given Options
We are given four options to distinguish between aldehydes and ketones. Let's analyze each option:

1. **Saturated solution of sodium bisulphite (NaHSO3)**:
- Aldehydes react with sodium bisulphite to form an addition compound.
- Some ketones (like acetone and methyl ketones) also react, but those with more than three carbon atoms do not.
- Conclusion: This reagent is not definitive for distinguishing between aldehydes and ketones.

2. **2,4-Dinitrophenylhydrazine (2,4-DNPH)**:
- Both aldehydes and ketones react with 2,4-DNPH to form hydrazones.
- Conclusion: This reagent does not distinguish between aldehydes and ketones.

3. **Tollens' reagent (Ammonical silver nitrate)**:
- Aldehydes react with Tollens' reagent to produce a silver mirror (Ag) due to the reduction of silver ions.
- Ketones do not react with Tollens' reagent.
- Conclusion: This reagent can distinguish between aldehydes (positive test) and ketones (negative test).

4. **Baeyer's reagent (KMnO4)**:
- Both aldehydes and ketones can be oxidized by KMnO4 to form carboxylic acids.
- Conclusion: This reagent does not distinguish between aldehydes and ketones.

### Step 3: Identify the Correct Answer
Based on the analysis, the correct answer to the question "Aldehydes and ketones may be distinguished by using" is **Tollens' reagent**.

### Final Answer:
**Tollens' reagent (Ammonical silver nitrate)** is the correct answer, as it distinguishes between aldehydes and ketones by producing a silver mirror with aldehydes but not with ketones.

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