Ionic Equilibrium

Three reactions involving $$H_2PO_4^−$$ are given below : (i) H₃PO₄ + H₂O $$\to$$ H₃O⁺ + $$H_2PO_4^−$$ (ii) $$H_2PO_4^−$$ + H₂O $$\to$$ $$HPO_4^{2−}$$ + H₃O⁺ (iii) $$H_2PO_4^−$$ + OH⁻ $$\to$$H₃PO₄ + O²⁻ In which of the above does $$H_2PO_4^−$$ act as an acid?