H4P2O6 i suppose :)
Possible P2O6 MeansNot: Phosphate because "anhydrous phophate" is P2O5 (most close to the original Q.) and "Phoshate" is (in chemistry) PO43-
Most chemical compound names are taken from what and how many atoms that they are made of. For instance, diphosphorus decoxide is di- (2) phosphorus dec- (10) oxide, or, P2O10.
When sodium hypophosphite reacts with copper sulfate, it forms copper hypophosphite and sodium sulfate. The balanced chemical equation for this reaction is: 3CuSO4 + 2NaH2PO2 → Cu3(P2O6)2 + 2Na2SO4.
it starts with a metal. look at your notes.