These chemical formulas can be explained as follows:

P2O5 - The chemical formula for diphosphorus pentoxide, a compound consisting of two atoms of phosphorus and five atoms of oxygen.

H3PO4 - The chemical formula for phosphoric acid, a compound consisting of three hydrogen atoms, one phosphorus atom, and four oxygen atoms.

Ca3(PO4)2 - The chemical formula for calcium phosphate, a compound consisting of three calcium atoms, two phosphate ions (each with one phosphorus atom and four oxygen atoms).