A : But-1-yne has acidic hydrogen but but-2-yne does not
R : In but-1-yne hydrogen atom is attached with sp hybridised carbon but no hydrogen is attached with sp hybridised carbon in-but-2-yne.

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 assertion-reason question regarding but-1-yne and but-2-yne, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Understand the Structures of But-1-yne and But-2-yne
- **But-1-yne (C4H6)**: The structure is CH3-CH2-C≡C-H. In this compound, there is a terminal alkyne, meaning that the triple bond is at the end of the carbon chain, and there is a hydrogen atom attached to the sp-hybridized carbon.
- **But-2-yne (C4H6)**: The structure is CH3-C≡C-CH3. In this compound, the triple bond is between the second and third carbon atoms, and both sp-hybridized carbons are bonded to other carbon atoms, with no hydrogen atoms attached.

### Step 2: Analyze the Assertion (A)
- The assertion states that but-1-yne has an acidic hydrogen, while but-2-yne does not.
- **Acidic Hydrogen**: A hydrogen atom is considered acidic if it can be removed as a proton (H+) when the compound reacts with a base. In but-1-yne, the hydrogen attached to the sp-hybridized carbon can be released as a proton, making it acidic.

### Step 3: Analyze the Reason (R)
- The reason states that in but-1-yne, the hydrogen atom is attached to an sp-hybridized carbon, while in but-2-yne, no hydrogen is attached to an sp-hybridized carbon.
- **Hybridization**: In but-1-yne, the terminal carbon (sp-hybridized) has one hydrogen attached, which contributes to its acidity. In but-2-yne, both sp-hybridized carbons are bonded to other carbons, meaning there are no hydrogen atoms that can be released.

### Step 4: Conclusion
- Both the assertion (A) and the reason (R) are true.
- The reason accurately explains why but-1-yne has an acidic hydrogen while but-2-yne does not.

### Final Answer
- The correct answer is that both assertion and reason are true, and the reason is the correct explanation of the assertion.