The molar mass of haemoglobin is 89600 g mot: The number of iron atoms per molecule of haemoglobin if the latter contains 0.25% iron by weight are 

Given. 100 g. haemoglobin contains iron = 0.25 g. 

89600 g haemoglobin contains iron

$=\frac{0.25g.}{100g.}\times 89600g=224g$

At. wt. of iron = 56 

$\therefore$ no. of atoms of Fe per molecule haemoglobin

$=\frac{224}{56}=4$ atoms

$\therefore$ 1 molecule of haemoglobin contains Fe atoms = 4