Reaction mixtures yielding acidic gases like HCl

Steps:

• Define acidic gas as one dissolving in water to form an acid (e.g., HCl, SO2).
• Analyze A: CaO (base) reacts with NH4NO3 to release NH3 gas (basic).
• Analyze B: NH3(aq) + HCl(aq) forms NH4Cl solution (no gas).
• Analyze C: KCl + conc. H2SO4 produces HCl gas (acidic).
• Analyze D: Na2O + H2O yields NaOH solution (no gas).

Why C is correct:

• Concentrated H2SO4 displaces HCl from KCl via KCl + H2SO4 → KHSO4 + HCl(g); HCl is acidic as it forms H+(aq) + Cl-(aq).

Why the others are wrong:

• A produces NH3 gas, which is basic (forms NH4OH).
• B is acid-base neutralization yielding no gas.
• D produces alkaline NaOH solution with no gas.

Final answer: C