The conjugate base has been the proton acceptor in the chemical reaction. The conjugate base in the given reaction has been [tex]\rm HPO_4^{2-}[/tex].
The chemical reaction has been the reaction in which the change in the reactant resulted in the product with distinctive properties.
The given reaction has been:
[tex]\rm NH_4\;+HPO_4^{2-}\;\rightarrow\;NH_3\;+\;H_2PO_4^-[/tex]
In the given reaction, the ammonia has been the proton donor, while [tex]\rm HPO_4^{2-}[/tex] has been the proton acceptor. Thus, the conjugate base in the reaction has been [tex]\rm HPO_4^{2-}[/tex]. Thus, option C is correct.
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