Gold crystallizes in the FCC lattice. Calculate the approximate number of the unit cells in 2 mg of gold (atomic mass of gold is 197 u)

197g of Gold contains 6.022*10^23 gold atoms
so 2mg of gold will have x gold atoms ie
2mg/1000=0.002g*6.022*10^23/197 gold atoms
=6.1137*10^18 gold atoms .
1 unit cell of fcc lattice contains 4 atoms .
so number of unit cell =6.1137*10^18 divided by 4
=1.5*10^18 unit cells