Which of the following statement(s) is/are correct:

Options

A. (a) Hydrogenation of but-2-yne in the presence of Lindlar's catalyst yields cis-but-2-ene.
B. (b) Hydrogenation of pent-2-yne in the presence of P-2 catalyst yields trans-pent-2-ene.
C. (c) Hydrogenation of pent-2-yne in the presence of K (potassium) and liquid `NH_3` yields trans-pent-2-ene.
D. (d) Hydrogenation of but-2-yne in the presence of `LiAlH_4` yields cis-but-2-ene.

Explanation

To determine which of the statements regarding the hydrogenation of alkynes are correct, we will analyze each statement step by step.

### Step 1: Analyze Statement A
**Statement A:** Hydrogenation of but-2-yne in the presence of Lindlar's catalyst yields cis-but-2-ene.

- **Hydrogenation Process:** But-2-yne (C4H6) can be hydrogenated using Lindlar's catalyst, which is a poisoned palladium catalyst. This catalyst facilitates the addition of hydrogen (H2) to the triple bond of but-2-yne, resulting in the formation of a cis-alkene.
- **Product Formation:** The product formed will have both methyl groups on the same side, resulting in cis-but-2-ene.

**Conclusion for Statement A:** This statement is correct.

### Step 2: Analyze Statement B
**Statement B:** Hydrogenation of pent-2-yne in the presence of Pt catalyst yields trans-pent-2-ene.

- **Hydrogenation Process:** Pent-2-yne (C5H8) can be hydrogenated using a platinum (Pt) catalyst. However, platinum is a non-poisoned catalyst that allows for syn addition, leading to the formation of a cis-alkene.
- **Product Formation:** The product formed will be cis-pent-2-ene, not trans-pent-2-ene.

**Conclusion for Statement B:** This statement is incorrect.

### Step 3: Analyze Statement C
**Statement C:** Hydrogenation of pent-2-yne in the presence of K (potassium) and liquid NH3 yields trans-pent-2-ene.

- **Hydrogenation Process:** When pent-2-yne is hydrogenated in the presence of potassium and liquid ammonia, this reaction leads to anti-addition of hydrogen across the triple bond.
- **Product Formation:** The product formed will be trans-pent-2-ene.

**Conclusion for Statement C:** This statement is correct.

### Step 4: Analyze Statement D
**Statement D:** Hydrogenation of but-2-yne in the presence of NiAlH4 yields cis-but-2-ene.

- **Hydrogenation Process:** But-2-yne can be hydrogenated using NiAlH4, which is a strong reducing agent. However, this reaction typically leads to the formation of a trans-alkene due to the nature of the addition.
- **Product Formation:** The product formed will be trans-but-2-ene, not cis-but-2-ene.

**Conclusion for Statement D:** This statement is incorrect.

### Final Conclusion
- **Correct Statements:** A and C are correct.
- **Incorrect Statements:** B and D are incorrect.

### Summary of Correct Statements:
- Statement A: Correct
- Statement B: Incorrect
- Statement C: Correct
- Statement D: Incorrect