The problem described above is a simple conversion problem. To determine the number of moles of a substance given the number of particles of a substance, we use the Avogadro's number. It represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of ions, atoms or molecules into number of moles. We do as follows:
4.05 x 10^22 atoms of iron ( 1 mol iron / 6.022 x 10^23 atoms iron) = 0.0673 moles of iron
Therefore, 4.05 x 1022 atoms of iron is equal to 0.0673 moles of iron.