Which of the following equations give ionic product of water?
(i) $ { NH_{3(aq)} + H_2 O <=> NH^+_{4(aq)} + OH^{-}_{(aq)}}$
(ii) $ { NH^+_{4(aq)} + H_2 O <=> H_3O^+ + NH_{3(aq)}}$
(iii) $ { NH^{-}_{2(aq)} + H_2 O <=> NH_{3(aq)} + OH^-}$
(iv) $ { NH_{3(aq)} + OH^{-}_{(aq)} <=> NH^{-}_{2(aq)} + H_2O}$