Hemoglobin contains 0.25% iron by weight. The molecular weight of hemoglobin is 89600. Calculate number of iron per molecular weight of compound?

0.25 % by mass means:

0.25 gms of iron in 100 gms haemoglobin.

therefore in 89600 gms i.e. 1 mole of haemoglobin contains:  0.25 x 89600 = 896 x 0.25 = 224 gms of fe

                                                                                             100

But 1mole of Fe i.e. 56 gms comtains 6.023 x 10²³ ( Avogadro number. N_A) atoms.

therefore 224 gms of Fe will contain:  224 x 6.023 x 10²³  = 2.409 x 10²⁴ atoms.

                                                               56