Answer: Fe
2 Fe ( s ) iron + 3 Cl 2 ( g ) chlorine gas → 2 FeCl 3 ( s ) iron trichloride
4 divided by 2 but times by 3 will give you the moles of cl2 needed to fully use the 4 mol of fe
thus 6 moles of cl2 are needed
thus fe is the limitjng reagent because after 6 mol of cl2 are used to expend the 4 mol fe. (7-6)=1 mol of cl2 will be in excess.