Hemoglobin contains $0.25\%$ of iron by weight. If molecular weight of hemoglobin is $89600$, how many iron atoms are present in each hemoglobin molecules ?

$0.25\%$ means $0.25 g$ in $100 g$

$100 g$ of hemoglobin contains $0.25 g$ of iron

Then for $89600 g$ of hemoglobin contains $=89600\times \frac{0.25}{100}=224 g$

The atomic mass of iron is $56$

Therefore no. of gram atoms of iron $\left(Fe\right)=224/56=4$

Each hemoglobin contains 4 iron atoms. 

Hence, the correct option is D.