What is the maximum amount in moles of P2O5 that can theoretically be made from 186 g of P4 and excess oxygen?

Molar mass of P₄ = 31.0 × 4 = 124.0 g/mol
Number of moles of P₄ reacted = (186 g) / (124.0 g/mol) = 1.50 mol

The balanced equation for the reaction :
P₄ + 5O₂ → 2P₂O₅
Mole ratio P₄ : P₂O₅ = 1 : 2

Maximum amount of moles of P₂O₅ made = (1.50 mol) × 2 = 3.00 mol

Moles of P2O5.....

Reaction of P4(s) and O2(g) to make "P2O5", which is actually P4O10. P2O5 is merely the empirical formula. The product actually consists of molecules of P4O10 which are linked together to make the solid.

P4(s) + 5O2(g) --> P4O10(s)
186g ....excess ........?mol

186g P4 x (1 mol P4 / 123.88g P4) x (1 mol P4O10 / 1 mol P4) = 1.50 mol P4O10 .... or .... 3.00 mol "P2O5"

And if you wanted the mass....

186g P4 x (1 mol P4 / 123.88g P4) x (1 mol P4O10 / 1 mol P4) x (283.88g P4O10 / 1 mol P4O10) = 426g P4O10.