Which of the following alkynes react with sodium in liquid ammonia ?
(i) Propyne (ii) But-2-yne (iii) Pent-3-yne (iv) Hex-1-yne

Explanation

To determine which of the given alkynes react with sodium in liquid ammonia, we need to identify the terminal alkynes among the options provided. Terminal alkynes have a hydrogen atom attached to one of the carbon atoms involved in the triple bond, which makes the hydrogen acidic.

Let's analyze each option step by step:

### Step 1: Identify the structure of each alkyne
1. **Propyne (CH₃C≡CH)**: This is a three-carbon alkyne with a terminal triple bond. The structure shows that there is a hydrogen atom attached to the carbon at the end of the triple bond.

2. **But-2-yne (CH₃C≡CCH₃)**: This is a four-carbon alkyne with the triple bond between the second and third carbon atoms. There are no hydrogen atoms attached to the carbons involved in the triple bond, making it a non-terminal alkyne.
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