Lewis base: is a donor of an electron pair (i.e., lone pair of electrons) For H2PO4^-, ClO^- and SO3^2-, the O atom and the Cl atom bear lone pair of electrons. Thus, all these three may behavior as Lewis bases. Solution Lewis base: is a donor of an electron pair (i.e., lone pair of electrons) For H2PO4^-, ClO^- and SO3^2-, the O atom and the Cl atom bear lone pair of electrons. Thus, all these three may behavior as Lewis bases..