Assertion. Addition of `H_2O` to acetylene occurs in presence of dil. `H_2SO_4` and `HgSO_4` to give acetaldehyde
Reason It is an example of electrophilic addition reaction

Options

A. If both assertion and reason are true, and reason is the true explanation of the assertion.
B. If both assertion and reason are true, but reason is not the true explanation of the assertion.
C. If assertion is true, but reason is false.
D. If both assertion and reason are false

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the addition of water (H₂O) to acetylene (C₂H₂) occurs in the presence of dilute sulfuric acid (H₂SO₄) and mercuric sulfate (HgSO₄) to produce acetaldehyde (CH₃CHO).
- This reaction is known as hydration of acetylene.

2. **Reaction Mechanism**:
- Acetylene (C₂H₂) is treated with water in the presence of dilute H₂SO₄ and HgSO₄.
- The mercuric ion (Hg²⁺) acts as an electrophile and coordinates with the triple bond of acetylene, forming a mercuric acetylide intermediate.
- The intermediate then undergoes nucleophilic attack by water (H₂O), leading to the formation of an enol (vinyl alcohol).
- This enol can rearrange to form acetaldehyde (CH₃CHO) through tautomerization.

3. **Conclusion of the Assertion**:
- Therefore, the assertion is true: the addition of H₂O to acetylene in the presence of dilute H₂SO₄ and HgSO₄ indeed gives acetaldehyde.

4. **Understanding the Reason**:
- The reason states that this reaction is an example of an electrophilic addition reaction.
- In this reaction, the electrophile (Hg²⁺) attacks the electron-rich triple bond of acetylene, which is characteristic of electrophilic addition reactions.

5. **Conclusion of the Reason**:
- The reason is also true: the reaction is indeed an example of electrophilic addition.

6. **Evaluation of the Explanation**:
- While both the assertion and reason are true, the reason does not fully explain the mechanism because it overlooks the role of the nucleophile (water) that also participates in the reaction.
- Therefore, while the reason is true, it is not a complete explanation of the assertion.

### Final Answer:
- Both the assertion and reason are true, but the reason is not a correct explanation for the assertion.