The number of P-O-P bridges in the structures of phosphorus pentoxide and phosphorus trioxide is

Phosphorus pentoxide (P4O10) has a structure that consists of four phosphorus atoms in a tetrahedral arrangement, each bonded to five oxygen atoms. However, none of these oxygen atoms form P-O-P bridges. They are all terminal oxygens, meaning they only bond to one phosphorus atom.

Phosphorus trioxide (P4O6), on the other hand, has a structure where each of the four phosphorus atoms is bonded to three oxygen atoms. Two of these oxygens are terminal, and one forms a P-O-P bridge. Therefore, there are four P-O-P bridges in phosphorus trioxide.

So, the number of P-O-P bridges in the structures of phosphorus pentoxide and phosphorus trioxide is 0 and 4, respectively.