Bases and ammonium salts reactions

Steps:

• Identify gas from base + ammonium salt: NH₄⁺ + OH⁻ → NH₃ + H₂O, ammonia gas.
• Test ammonia on litmus: turns red litmus blue, no effect on blue litmus.
• Analyze pH change: base adds OH⁻, shifts equilibrium NH₄⁺ ⇌ NH₃ + H⁺ right, reduces H⁺, raises pH.
• Review definitions: alkali is soluble base; neutralization involves base accepting H⁺ from acid.

Why B is correct:

• Base reacts with NH₄⁺ to form NH₃ + H₂O, consuming H⁺ ions and increasing solution pH per equilibrium law.

Why the others are wrong:

• A: Ammonia gas turns damp red litmus blue, not blue litmus (which stays blue).
• C: Aqueous sodium hydroxide is both a base and an alkali (soluble in water).
• D: Neutralization has acid donating proton to base, forming salt + water.

Final answer: B