Density of a unit cell is the same as the density of the substances. So, if the density…

Density of a unit cell is the same as the density of the substances. So, if the density of the substance is known, we can calculate the number of atoms or dimesions of the unit cell. The density of the unit cell is related to its mass (M), number of atoms per unit cell (Z), edge length (a in cm), and Avogadro’s constant N_A as :
\(\rho=\frac{\mathrm{Z} \times \mathrm{M}}{\mathrm{a}^{3} \times \mathrm{N}_{\mathrm{A}}}\) 
The number of atoms present in 100 g of a bcc crystal (density = 12.5 g cm^–3) having cell edge 200 pm is