Which of the following gases is evolved as a byproduct (A) in the...

The reaction between ethyne and lithium amide is an acid-base reaction.

Ethyne has acidic hydrogen atoms due to the sp hybridized carbon atom. Lithium amide is a strong base.

The amide ion abstracts a proton from ethyne to form lithium acetylide and ammonia gas.

$\text{HC}\equiv\text{CH} + \text{LiNH}_2 \rightarrow \text{HC}\equiv\text{C}^-\text{Li}^+ + \text{NH}_3$

The byproduct (A) is $\text{NH}_3$.

Answer: $\text{NH}_3$