Ammonia as a weak base in water

Steps:

• Ammonia (NH₃) dissolves in water as neutral molecules.
• NH₃ partially reacts with H₂O to form NH₄⁺ and OH⁻.
• The equilibrium NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ shows both species coexist.
• No complete ionization occurs due to weak basicity.

Why B is correct:

• Aqueous ammonia is a weak base solution where NH₃ partially ionizes to NH₄⁺ via NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, producing both species.

Why the others are wrong:

• A: Amide ions (NH₂⁻) require strong bases like NaNH₂, not present in dilute aqueous NH₃.
• C: Un-ionized NH₃ molecules remain due to incomplete dissociation.
• D: Ionization produces some NH₄⁺ alongside excess NH₃.

Final answer: B