(d)
Molecular mass of $(CHCOO)_{2}Fe$=170
$\therefore$ In 100 g $(CHCOO)_{2}Fe$, iron present $= \frac{56}{170} \times 100$ mg
$= 32.9$ mg
Since, this quantity of Fe is present in 400 mg of capsule,
$\therefore$ % of Fe in capsule $= \frac{32.9}{400} \times 100 = 8.2\%$