Yes, NH3 (ammonia) is a base. It is considered a weak base because it does not completely dissociate in water. When NH3 is dissolved in water, it reacts with water molecules to form ammonium ions (NH4+) and hydroxide ions (OH-). This reaction can be represented by the following equation:
NH3 + H2O ⇌ NH4+ + OH-
The presence of hydroxide ions (OH-) in the solution makes it basic. However, since the reaction does not go to completion, only a small fraction of NH3 molecules react with water, making it a weak base.