Question: how many moles of carbon monoxide are needed to react completely with 1.75?
Answer: According to your equation, for every mole of iron oxide (Fe2O3), it takes 3 moles of carbon monoxide (CO). So for 1.75 moles, it takes 3 times as many moles of CO. 1.75 x 3 = 5.25 moles of CO.