The compound in question is FePO4, which is commonly referred to as iron(II) phosphide. However, this name is incorrect for two main reasons.
Firstly, the Roman numeral (II) in the name indicates that iron has a +2 oxidation state. Yet, in the compound FePO4, iron actually has a +3 oxidation state. This is derived from the fact that the phosphate ion (PO4) has a -3 charge. To balance the charge, iron must indeed be in the +3 state.
Secondly, the name ‘phosphide’ suggests that the phosphorus is in a -3 oxidation state, which is characteristic of simple phosphides. Since we are dealing with phosphate (PO4), where phosphorus is at a +5 oxidation state, ‘phosphide’ is not appropriate here either.
Thus, the correct name for the compound FePO4 is iron(III) phosphate. This correctly reflects the +3 oxidation state of iron and the nature of the phosphate group present in the compound.