Ammonia gas from base-ammonium salt reaction

Steps:

• The gas turns red litmus blue, identifying it as ammonia (NH3), an alkaline gas.
• Ammonium nitrate solution contains NH4+ ions; heating with a base decomposes it to release NH3.
• A basic solid R must react with NH4NO3 to form the hydroxide that liberates NH3.
• Sodium oxide (Na2O) is basic and fits, as it forms NaOH upon hydration, driving the reaction.

Why C is correct:

• Na2O + H2O → 2NaOH; then 2NaOH + 2NH4NO3 → 2NaNO3 + 2NH3 + 3H2O, producing ammonia gas.

Why the others are wrong:

• A. Aluminium chloride is acidic (AlCl3 hydrolyzes to form HCl), suppressing ammonia release.
• B. Magnesium chloride is a neutral salt, unable to generate a base for NH3 evolution.
• D. Phosphorus oxide (P4O10) is acidic, forming phosphoric acid that neutralizes rather than liberates NH3.

Final answer: C