3.45 x 10^22 atoms of Fe in 6 L of blood.
First calculate how many grams of hemoglobin as in 6 L of blood
15.4 g /100 ml * 6L = 15.4 g / 0.1 L * 6 L = 924 g
Now calculate how many moles of hemoglobin you have by dividing the mass of hemoglobin by its molar mass
924 g / 64500 g/mol = 0.014326 moles
Since there's 4 Fe atoms per hemoglobin molecule, multiply by 4
0.014326 * 4 = 0.057304 moles of Fe atoms.
Finally, multiply the number of moles of Fe atoms by avogadro's number
0.057304 * 6.0221409 x 10^23 = 3.45093 x 10^22
