Explanation

(b)
This reaction is utilized for the preparation of higher alkynes
$CH_{3} - C \equiv C - H + Na\overset{Liq.NH_{3}}{\rightarrow}CH_{3} - C \equiv C - Na$
Propyne
$CH_{3} - C \equiv C - Na + BrCH_{3} \rightarrow CH_{3} - C \equiv C - CH_{3} + NaBr$
_{But-2-yne}