For Which of the Following Equilibria Does K_c Correspond to the Acid-Dissociation

Multiple Choice

For which of the following equilibria does K_c correspond to the acid-dissociation constant,K_a,of H₂PO₄^-?

A) H₂PO₄^-(aq) + H₃O⁺(aq) H₃PO₄(aq) + H₂O(l)
B) H₂PO₄^-(aq) + H₂O(l) H₃PO₄(aq) + OH^-(aq)
C) H₂PO₄^-(aq) + H₂O(l) H₃O⁺(aq) + HPO₄^2-(aq)
D) H₃PO₄(aq) + H₂O(l) H₃O⁺(aq) + H₂PO₄^-(aq)
E) HPO₄^2-(aq) + H₂O(l) H₂PO₄^-(aq) + OH^-(aq)