Why ammonia gas only acts as a week alkali in the presence of water?

Ammonia gas acts as a weak alkali in the presence of water because it partially ionizes to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻). This ionization process is not complete, which means that only a small fraction of ammonia molecules contribute to the increase in hydroxide ion concentration, resulting in weak alkalinity. The equilibrium established in the solution further limits the extent of ionization, making ammonia a weak base compared to strong alkalis that fully dissociate in water.