1.
Three reactions involving H2PO4−H_2PO_4^- are given below:
(i) H3PO4+H2O→H3O++H2PO4−H_3PO_4 + H_2O \rightarrow H_3O^+ + H_2PO_4^-
(ii) H2PO4−+H2O→HPO42−+H3O+H_2PO_4^- + H_2O \rightarrow HPO_4^{2-} + H_3O^+
(iii) H2PO4−+OH−→H3PO4+O2−H_2PO_4^- + OH^- \rightarrow H_3PO_4 + O^{2-}
In which of the above does H2PO4−H_2PO_4^- act as an acid?