Question: how many molecules of carbon monoxide are needed to react with excess iron?
Answer: Note that the front number "2Fe" and "3CO" represents the number of molecules used as mole ratio. The mole ratio between Fe:CO is 2:3. If 2 moles of iron (Fe) gives you 3 moles of carbon monoxide (CO), then 2.003577818 moles of 2Fe must give you: [2.003577818 moles ÷ 2, then × 3] = 3.0053667263 moles of CO.