Final answer:
The conjugate acid-base pairs in the given equilibrium are H₂C₂O₄/HC₂O₄⁻ and HPO₄²⁻/H₂PO₄⁻.
Step-by-step explanation:
In the given equilibrium H₂C₂O₄(aq) + HPO₄²⁻ (aq) → HC₂O₄⁻(aq) + H₂PO₄⁻(aq), a conjugate acid-base pair is a pair of substances that differ by the gain or loss of a single proton (H+). In this reaction, HC₂O₄⁻ is the base that is the conjugate of the acid H₂C₂O₄, and H₂PO₄⁻ is the acid that is the conjugate of the base HPO₄²⁻. Thus, the conjugate pairs are H₂C₂O₄/HC₂O₄⁻ and HPO₄²⁻/H₂PO₄⁻.