The chemical reaction would be:
5O2 + P4 = 2 P2O5
We start with the initial amount of the limiting reactant which is oxygen and relate the substances from the chemical reaction to determine the maximum amount of P2O5 produced.
moles O2 = 144 g / 32 g/mol = 4.5 mol
moles P2O5 = 4.5 ( 2 / 5 ) = 1.8 mol P2O5
