How do you do this? (atomic radius)?

Question

Nickel has a face-centered cubic unit cell. The density of nickel is 6.84 grams per centimeter cubed. What is the atomic radius, in angstroms, of nickel?
Atomic weight of Nickel = 58.71 g/mol

Answer 1

The face centered cubic has lattice points on the faces of the cube of which each unit cube gets exactly one half contribution, in addition to the corner lattice points, giving a total of 4 atoms per unit cell.
Molar mass of nickel: 58.6934g/mol
6.84 grams of nickel
= 0.1165 mole of nickel
= 7.018x10^22 atoms of nickel
= 1.754x10^22 unit cells of nickel (in one cubic centimeter)
= 2.598x10^7 unit cells along one direction (in 1cm)
==> unit cell has a side length of 3.848 Å
==> atomic radius = (3.848 Å)*sqrt(2)/4 = 1.36Å = 136 pm.

Answer 2

1.36

Answer 3

1.36