To find the answer to this question we will need first to set up some informations:
4 Fe + 3 O2 -> 2 Fe2O3, this is the balanced equation for the question
Now we will need the molar mass of each reactant, which will be:
Fe = 55.8 g/mol, since there are 4 Fe, then we will have 4*55.8 = 223.2 g/mol
O2 = 32 g/mol, since there are 3 O2, then we will have 3*32 = 96 g/mol
Now we know that in a regular reaction, we would need 4 moles of Fe and 3 moles of O2 to properly react, hence, 223.2 g/mol to react with 96.0 g/mol.
But in our question we only have 8.0 grams available, to find out how many of oxygen moles there are, we can do the following math:
96 g = 3 moles
8.0 g = x moles
x = 0.25 moles
Following the molar ratio, we have that 4 moles of iron react with 3 moles of oxygen, but now we have only 0.25 moles:
4 Fe = 3 O2
x Fe = 0.25 O2
x = 0.3 moles of Iron