H₃PO₃ Is a Diprotic Weak Acid $\rightleftharpoons$ H₃O⁺(aq) + H₂PO₃^-(aq)
B) H₂PO₃^-(aq) + H₂O(l)

H₃PO₃ is a diprotic weak acid. What is the balanced equilibrium defined as K_b2 of H₃PO₃?

A) H₃PO₃(aq) + H₂O(l) $\rightleftharpoons$ H₃O⁺(aq) + H₂PO₃^-(aq)
B) H₂PO₃^-(aq) + H₂O(l) $\rightleftharpoons$ H₃O⁺(aq) + HPO₃^2-(aq)
C) HPO₃^2-(aq) + H₂O(l) $\rightleftharpoons$ OH^-(l) + H₂PO₃^-(aq)
D) H₂PO₃^-(aq) + H₂O(l) $\rightleftharpoons$ OH^-(l) + H₃PO₃(aq)
E) HPO₃^2-(aq) + H₂O(l) $\rightleftharpoons$ OH^-(aq) + H₃PO₃(aq)