## Chemistry: An Atoms-Focused Approach

(a) In one mole of FeO, we have 1 mole of iron. (b) In Fe$_2$O$_3$, we have 2 moles of iron. (c) In Fe(OH)$_3$, we have 1 mole of iron. (d) In Fe$_3$O$_4$, we have 3 moles of iron.