Final answer:
NH₃ (ammonia) is a weak base as it only partially ionizes in aqueous solution, with about 0.4% of dissolved ammonia molecules dissociating into ions.
Step-by-step explanation:
NH3 (ammonia) is a weak base. In aqueous solution, ammonia only partially ionizes, indicating that it does not completely dissociate into ions when dissolved in water. The reaction of ammonia in water can be represented as NH3(aq) + H2O(ℓ) ⇌ NH4+(aq) + OH−(aq). This reaction shows that ammonia accepts a proton from water to form the ammonium ion and a hydroxide ion, making the solution slightly basic. However, as only about 0.4% of dissolved ammonia molecules dissociate at room temperature, it is considered a weak base rather than a strong base which would be completely ionized in solution.