Barium metal crystallizes in a body-centered cubic lattice (the Ba atoms are at the lattice points only). The unit cell edge length is 502 pm, and the density of the metal is 3.50 g/cm3. Using this information, calculate Avogadro's number. [First calculate the volume (in cm3) occupied by 1 mole of Ba atoms in the unit cells. Next calculate the volume (in cm3) occupied by one Ba atom in the unit cell. Assume that 68% of the unit cell is occupied by Ba atoms.]