`[A] overset("lindlar's")underset("catalyst")larr CH_(3) - C -= C -CH_(3) overset("Na in ")underset(liq. NH_3)rarr [B]`
[A] and [B] are respectively

Options

A. C is trans -2- butene
B. Both trans-2-butene
C. Trans, cis-2-butene
D. Both cis-2-butene

Explanation

To solve the question, we need to identify the compounds [A] and [B] based on the given reactions involving Lindlar's catalyst and sodium in liquid ammonia.

### Step-by-Step Solution:

1. **Identify Compound [A]:**
- The starting compound is given as CH₃ - C≡C - CH₃, which is 2-butyne (an alkyne).
- When 2-butyne undergoes partial hydrogenation in the presence of Lindlar's catalyst, it converts to a cis-alkene.
- The product of this reaction is cis-2-butene (cis-CH₃-CH=CH-CH₃).
- Therefore, [A] is 2-butyne (CH₃ - C≡C - CH₃).

2. **Identify Compound [B]:**
- The second part of the reaction involves the reduction of the same alkyne (2-butyne) using sodium in liquid ammonia.
- This reaction leads to the formation of a trans-alkene.
- The product of this reaction is trans-2-butene (trans-CH₃-CH=CH-CH₃).
- Therefore, [B] is trans-2-butene.

### Final Answer:
- [A] is 2-butyne (CH₃ - C≡C - CH₃).
- [B] is trans-2-butene (trans-CH₃-CH=CH-CH₃).