Chemistry and Chemical Reactivity (9th Edition)

$FeSO_4$
Molar masses: $FeSO_4: 151.91\ g/mol,\ Fe(C_6H_11O_7)_2: 446.14\ g/mol$ Since there's 1 mol of Fe per mol of compound in both of them and the mass ingested is the same, the one with the lower molar mass will have more atoms of iron.