Question: hpo42- can act as an acid and as a base?
Answer: HPO4–2 can accept two protons further(and becomes phosphoric acid, H3PO4), so according to Bronstd-Lowry theory it is an base. And also it can donate the last proton it i having to become phosphate ion,PO4–3, so it is acid also. practically there are many species that can act as both acids and base.