Bronsted-Lowry theory: Acid is a proton donor (H+) and base is a proton acceptor, i.e NH3(aq) + H2O (l) ⇌ NH4+ (aq) + OH-(aq) (In the left hand side, the H2O is donating a proton thus is the acid, and the NH3 receives a proton thus is the base)Lewis theory: Acid is an electron pair acceptor (electrophile) and a base is an electron pair donor (nucleophile), i.e SO3(g) + H2O (l) ⇌ H2SO4 (aq) (in the left side, the SO3 acts a lewis acid by accepting an electron pair and H2O acts as a lewis base by donating a pair of electrons)More specifically the bond formed is a coordinated covalent bond, as the e- pair shared amongst the two species (between the Oxygen atom and the sulfur atom).