Hello!
To find the number of moles in 4.5 x 10^25 atoms, we need to divide the total number of number by Avogadro's number. His number is 6.02 x 10^23 atoms. This number represents the number of atoms in one mole.
(4.5 x 10^25 atoms) / (6.02 x 10^23) ≈ 74.75083056
Using significant figures, there are about 75 moles in 4.5 x 10^25 atoms of nickel, which is choice D.
