Assertion. But-2-yne on reduction with `Na//NH_3(l)` gives trans-2-butene
Reason. To minimise interelectronic repulsions, the addition of electrons occurs on the opposite faces of the triple bond.

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 regarding the assertion and reason related to the reduction of but-2-yne with sodium in liquid ammonia, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- But-2-yne (C4H6) is an alkyne with a triple bond between the second and third carbon atoms. The structure can be represented as CH3-C≡C-CH3.

2. **Reduction Process**:
- The reduction of but-2-yne involves the addition of electrons to the triple bond. In this case, sodium (Na) in liquid ammonia (NH3) acts as a reducing agent.

3. **Formation of Trans-2-butene**:
- When but-2-yne is reduced, the electrons are added to the triple bond. Due to the nature of the reaction, the addition of electrons occurs on opposite faces of the triple bond. This leads to the formation of trans-2-butene (C4H8) as the major product.

4. **Explanation of the Assertion**:
- The assertion states that but-2-yne on reduction with Na/NH3(l) gives trans-2-butene. This is true because the reaction conditions favor the formation of the trans isomer.

5. **Understanding the Reason**:
- The reason provided states that to minimize interelectronic repulsions, the addition of electrons occurs on opposite faces of the triple bond. This is also true, as the trans configuration minimizes steric hindrance and electronic repulsion between the substituents.

6. **Conclusion**:
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the statement is valid.

### Final Answer:
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason is the correct explanation of the assertion.