Final answer:
The IUPAC name for HPO4²− is hydrogen phosphate, and it is amphoteric, able to act as both an acid and a base.
Step-by-step explanation:
The IUPAC name for HPO4²− is hydrogen phosphate. In the context of acid-base reactions, HPO4²− can act both as an acid, by donating a proton to form H3O+ and PO4³−, and as a base, by accepting a proton to form H2PO4−. This dual ability to donate and accept protons makes HPO4²− amphoteric. In an example where HPO4²− gains a proton, it becomes H2PO4−, also known as dihydrogen phosphate.