a,
$FeS: \%Fe=\dfrac{56.100}{88}=63,6\%$
$FeO: \%Fe=\dfrac{56.100}{72}=77,7\%$
$FeS_2: \%Fe=\dfrac{56.100}{120}=46,67\%$
$Fe_2O_3:\%Fe=\dfrac{56.2.100}{160}=70\%$
$Fe_3O_4:\%Fe=\dfrac{56.3.100}{232}=72,4\%$
Sắp xếp: $FeS_2 < FeS < Fe_2O_3 < Fe_3O_4 < FeO$
b,
$FeS: \%Fe=\dfrac{56.100}{88}=63,6\%$
$FeCl_3:\%Fe=\dfrac{56.100}{162,5}=34,46\%$
$FeSO_4: \%Fe=\dfrac{56.100}{152}=36,84\%$
$Fe_2(SO_4)_3:\%Fe=\dfrac{56.2.100}{400}=28\%$
$Fe(OH)_3:\%Fe=\dfrac{56.100}{107}=52,34\%$
Sắp xếp: $Fe_2(SO_4)_3<FeCl_3<FeSO_4<Fe(OH)_3<FeS$