Fe₂O₃ + 3CO → 2Fe + 3CO₂
moles of Fe₂O₃ = mass ÷ molar mass
= 100 g ÷ [(56 × 2) + (16 × 2)] g/mol
= 100 g ÷ 144 g/mol
= 0.694 mol
mole ratio of Fe₂O₃ : CO is 1 : 3
∴ if mole of Fe₂O₃ = 0.694 mol
then mole of CO = 0.694 × 3
= 2.083 mol
mass of CO = mole × molar mass
= 2.083 × (12 + 16) g/mol
≈ 58.33 g