Acid-base reactions in ammonium sulfide solution

Steps:

• NH3 and H2S form (NH4)2S(aq), dissociating to NH4+ and S2- in alkaline solution.
• Adding HCl provides H+, protonating S2- to HS- then H2S(g), so X is H2S.
• The resulting solution contains NH4+ and Cl- after H2S release.
• Adding NaOH to this solution deprotonates NH4+ to NH3(g), so Y is NH3.

Why C is correct:

• C matches X as H2S from sulfide protonation (S2- + 2H+ → H2S) and Y as NH3 from ammonium basification (NH4+ + OH- → NH3 + H2O).

Why the others are wrong:

• A: Y is not H2S, as basification does not regenerate sulfide gas.
• B: X is not NH3, since acidification targets S2- first, not NH4+.
• D: Neither gas is NH3; X comes from sulfide, not ammonia.

Final answer: C