Elemental S reacts with O2 to form SO3 according to the reaction:
2S+3O2→2SO3
A- How many O2 molecules are needed to react with 3.66 g of S?
B - What is the theoretical yield of SO3 produced by 3.66 g of S
mols S = grams/atomic mass = 3.66/32 = 0.114
Convert mols S to mols O2. Using the coefficients in the balanced equation that's 0.114 mols S x (3 mol O2/2 mols S) = 0.l72 mols O2.
You know there are 6.02E23 molecules in 1 mol O2 so how many molecules O2 are in 0.172 mols O2?
Post your work if you get stuck.