The conjugate acid of $H_2PO_4^-$ is

The ammonium ion $(NH_4^+)$ acts as:

Cis-butene dioic acid $\overset{K_{a_1}(-H^+)}{\longleftrightarrow} X_1^- \overset{K_{a_2}(-H^+)}{\longleftrightarrow} X_2^{2-}$
Trans-butene dioic acid $\overset{K'_{a_1}(-H^+)}{\longleftrightarrow} Y_1^- \overset{K'_{a_2}(-H^+)}{\longleftrightarrow} Y_2^{2-}$
The incorrect statement regarding the above information is:

The conjugate base of $H_3O^{+}$ is

Chloroplatinic acid is

$A$ substance containing hydrogen and releasing $H^{+}$ in aqueous medium is an acid. Identify the theory suggesting this concept from the following.