For bcc unit cell, the number (Z) of atoms per unit cell is 2.
The atomic mass (M) is 20 amu.
Density =Z×M(abc)
Here, a, b and c are the unit cell dimensions.
Density =2×20(0.5×10−9×0.2×10−9×0.1×10−9)
Density =4×1030amu/m3
Note: nm are converted to m by using the relationship 1 nm =10−9 m