Dihydrogen phosphate (H₂PO₄⁻) is amphiprotic, meaning it can act as both an acid and a base.

Here's why:

* As an acid: It can donate a proton (H⁺) to form the hydrogen phosphate ion (HPO₄²⁻):

H₂PO₄⁻ + H₂O ⇌ HPO₄²⁻ + H₃O⁺

* As a base: It can accept a proton (H⁺) to form phosphoric acid (H₃PO₄):

H₂PO₄⁻ + H₂O ⇌ H₃PO₄ + OH⁻

Whether dihydrogen phosphate acts as an acid or a base depends on the surrounding solution and its pH.