According to Arrhenius theory of acids and bases:
Acid : An acid is a substance which on dissolving in water gives rise to H+ ion as the only cation. For example, HCl, H2 SO4 , H2 CO3etc.
Base : A base is a substance which on dissolving in water gives rise to the OHion as the only anion. For example, NaOHCa(OH)2etc.