To distinguish between formaldehyde and acetaldehyde, we require

Options

A. Tollen's reagent
B. Fehling's Solution
C. Schiff's reagent
D. Caustic soda Solution

Answer

To distinguish between formaldehyde (HCHO) and acetaldehyde (CH3CHO), we can utilize the different reactivity of these aldehydes in the presence of a strong base like sodium hydroxide (NaOH), also known as caustic soda. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
- **Formaldehyde**: HCHO
- **Acetaldehyde**: CH3CHO

### Step 2: Analyze the Structure
- Formaldehyde does not have any alpha hydrogen atoms (hydrogens attached to the carbon adjacent to the carbonyl group).
- Acetaldehyde has three alpha hydrogen atoms (the three hydrogens attached to the methyl group, CH3).

### Step 3: React with Sodium Hydroxide (NaOH)
- When formaldehyde is treated with NaOH, it undergoes a **Cannizzaro reaction** because it lacks alpha hydrogens. This reaction leads to the disproportionation of formaldehyde into methanol and formic acid.

- When acetaldehyde is treated with NaOH, it undergoes **aldol condensation** due to the presence of alpha hydrogens. This reaction leads to the formation of a β-hydroxy aldehyde, which can further dehydrate to form an α,β-unsaturated aldehyde.

### Step 4: Conclusion
- By adding NaOH to both compounds, we can observe different reactions:
- Formaldehyde will not undergo aldol condensation and will instead undergo the Cannizzaro reaction.
- Acetaldehyde will undergo aldol condensation due to the presence of alpha hydrogens.

Thus, the reagent required to distinguish between formaldehyde and acetaldehyde is **sodium hydroxide (NaOH)**.

### Final Answer
The answer to the question is **NaOH (caustic soda solution)**.

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