A and D respectively are:

The correct answer is option 3. But-2-ene; Butan-2-one.

The initial reactant will react with alc. KOH via \(E_2\) mechanism to produce but-2-ene (A). Then (A) will undergo bromination reaction to produce 2,3-Dibromobutane (B). The compound (B) will react with alc. KOH followed by reaction with \(NaNH_2\)to produce But-2-yne (C). The compound (C) reacts with \(H_2O\), \(Hg^{2+}/H^+\) to give Butan-2-one (D).