Answer. According to Arrhenius concept, bases are only those compounds which contain (OH-) ions. As NH3 does not contain any (OH-) ion therefore, it is not an Arrhenius base. While Bronsted Lowry base is a substance that can accept a proton (H+) from another substance. For example, NH3 accepts a proton from water such as
H2O(1) + NH3(aq) NH4+(aq) + OH-(aq)
As NH3 can accept a proton so it is a Bronsted-Lowry base.