GIVEN :-

Lattice system = FCC
Edge of unit cell, a = 3.52 A⁰ = 3.52 x 10^-10 m
M = 58.71 kg / k. mol
N = 6.02 x 10²⁶ atoms / k. mol.
and For FCC, n = 4

Density = nM / N (a)³
      = [( 4 atoms) (58.71 kg / k. mol)] / [6.02 x 10²⁶ atoms / k. mol) (3.52 x 10^-10m)³]
      = [(234.84 / 262.56)] x 10⁴ kg / m³
      = 8944 kg / m³