A : Ethanal undergoes aldol condensation.
R : Ethanal has four `alpha`-H atoms.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4).

Answer

To solve the question, we need to analyze the assertion and reason provided:

**Assertion (A): Ethanal undergoes aldol condensation.**
**Reason (R): Ethanal has four alpha-H atoms.**

### Step-by-Step Solution:

1. **Understanding Aldol Condensation:**
- Aldol condensation is a reaction between aldehydes or ketones that have at least one alpha-hydrogen atom. This reaction involves the formation of a β-hydroxy aldehyde or ketone, which can further dehydrate to form an α,β-unsaturated carbonyl compound.

2. **Identifying Ethanal:**
- Ethanal (acetaldehyde) has the chemical formula CH₃CHO. It consists of a carbonyl group (C=O) and a methyl group (CH₃).

3. **Counting Alpha-Hydrogens:**
- Alpha-hydrogens are the hydrogen atoms attached to the carbon atom adjacent to the carbonyl carbon. In the case of ethanal, the carbon adjacent to the carbonyl (C=O) is the methyl group (CH₃), which has three hydrogen atoms.
- Therefore, ethanal has **three alpha-hydrogens**, not four.

4. **Conclusion on Assertion and Reason:**
- The assertion that ethanal undergoes aldol condensation is true because it has alpha-hydrogens.
- The reason provided states that ethanal has four alpha-hydrogens, which is incorrect since it actually has three.
- Therefore, while the assertion is true, the reason is false.

### Final Answer:
- The assertion (A) is true, but the reason (R) is false.