Haemoglobin contains 0.33% of fe by wt. the molecular mass of haemoglobin is approximately 67200. the no. of fe atoms ( at wt. of fe 56) present in one molecule of haemoglobin is

a) 6
b) 1
c) 4
d) 2

p. s. i don't want to get the answer or the formula ( i know them) i need to know the procedure of doing such questions : )

We are given the total mass of the molecule and percentage of iron within it. First, we calculate the mass of iron in the molecule:
67,200 x 0.0033 = 221.76 g
This is the total mass of iron. We know that each atom of iron weighs 56g
If we divide the total mass of iron by the mass of one atom of iron, we can get the number of atoms of iron. So:
221.76/56
= 3.96 ≈ 4 atoms
The answer is C

Similar questions will be handled in this way, where you first calculate the amount (mass in this case) of substance in interest and then divide by the unit amount (atomic mass in this case) of the substance to find the number of units (atoms in this case).