Haemoglobin contains 0.33% of iron by weight. The molecular mas of haemoglobin is about 67200. the number of iron atoms (atomic mass of Fe=56) present in molecule of haemoglobin is:
Percentage of Fe=0.33 % molecular weight of haemoglobin
Weight of Fe present = 0.33100×67200 = 221.8
One Fe weighs 55.8 g
Therefore, 221.855.8 =4