69.3 g
First, determine the molar masses involved:
Atomic weight iron = 55.845
Atomic weight carbon = 12.0107
Atomic weight oxygen = 15.999
Molar mass Fe2O3 = 2 * 55.845 + 3 * 15.999 = 159.687 g/mol
Molar mass CO = 12.0107 + 15.999 = 28.0097 g/mol
Determine how many moles of each reactant we have
Moles Fe2O3 = 189 g / 159.687 g/mol = 1.18356535 mol
Moles CO = 63.0 g / 28.0097 g/mol = 2.249220806 mol
For every mole of Fe2O3, we need 3 moles of CO. So let's see how many moles of Fe2O3 is consumed by dividing moles CO by 3.
2.249220806 mol / 3 = 0.749740269 mol
So we'll be consuming 0.749740269 moles of Fe2O3, subtract that from what we started with
1.18356535 mol - 0.749740269 mol = 0.433825081 mol
Now multiply by the molar mass of Fe2O3
0.433825081 mol * 159.687 g/mol = 69.27622574 g
Rounding to 3 significant figures gives 69.3 g