How many fe atoms are contained in 787 g of fe?

To determine the number of atoms in a certan mass of a substance, we need to convert the mass into units of moles by dividing the molar mass or the atomic mass of the substance. Then, we multiply the Avogadro's number which number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. We do as follows:

787 g Fe (1 mol / 55.85 g) (6.022x10^23 atoms / 1 mol) = 8.49x10^24 atoms Fe