The radius of a platinum atom is 139 pm. How many platinum atoms would have to be laid side by side to span a distance of 1.39 mm?

5x10⁶ atoms of platium have to be laid side by side

Explanation:

1 atom of platium has a radius of 139pm = 139x10⁻¹²m. The distance that occupies 1 atom of platinum is 2 times its ratio:

139x10⁻¹²m*2 = 2.78x10⁻¹⁰m

Assuming there is no distance between to atoms of platinum, just its ratio. The amount of atoms necessary to occupy  1.39mm = 1.39x10⁻³m is:

1.39x10⁻³m / 2.78x10⁻¹⁰m =

personal, she chose to do it.