Gas Formation in Acid-Base and Displacement Reactions

Steps:

• Identify reaction for NaOH(aq) + NH4Cl(s): Forms NH3 gas via NH4+ + OH- → NH3(g) + H2O.
• Identify reaction for H2SO4(aq) + NH4Cl(s): Produces NH4HSO4(aq), no gas evolves.
• Identify reaction for H2SO4(aq) + Mg(s): Single displacement yields H2 gas via Mg + 2H+ → Mg2+ + H2(g).
• Match pattern: Gas in mixtures 1 and 3, none in 2, corresponding to option B.

Why B is correct:

• Matches gas production in first (ammonia from base-ammonium salt) and third (hydrogen from metal-acid) reactions, per standard double displacement and single replacement rules.

Why the others are wrong:

• A incorrectly labels solids without indicating gas formation pattern.
• C wrongly shows no gas in any mixture, ignoring NH3 and H2 evolution.
• D misses gas in first mixture, underestimating base-ammonium reaction.

Final answer: B