Originally Posted by starrysky
The atomic radius of metal X is 1.50 × 102 picometers (pm) and a crystal of metal X has a unit cell that is facecentered cubic. Calculate the density of metal X (atomic weight = 42.3 g/mol).

The main concept here is to find the density of the material...ie. from a single unit cell. So for an FCC crystal how many atoms of X are in the unit cell? What are the dimensions of the unit cell? So now you know the density in terms of # of atoms/volume in a unit cell. The rest is unit conversions.
Does this help or do you need more?
Dan