A 400 mg iron capsule contains 100 mg of ferrous fumarate, (CHCOO)₂Fe. The percentage of iron present in it is approximately

Molecular weight of (CHCOO)₂Fe = 170
Fe present in 100 mg of (CHCOO)₂Fe = 17

$=\frac{56}{170}\times 100\mathrm{mg}=32.9\mathrm{mg}$

This is present in 400 mg of capsule
% of Fe in capsule $=\frac{32.9}{400}\times 100=8.2$.