Question

How many atoms per unit cell (z) are present in bcc unit cell?

Answer 1

In bcc unit cell, $1$ atom is present at the center of the body and $8$ atoms are present at the $8$ corners of body. The atom at the center of body contributes fully to the unit cell. The contribution of each corner atom to the unit cell is one eight. Hence, the total number of atoms in the unit cell is $\frac{1}{8}\times 8+1=2$.