4 atoms per unit cell
Work Step by Step
As can be seen in the diagram, each of the 8 atoms on the corners of the cell contributes 1/8 of its volume. Each of the 6 atoms at the center of each face contributes 1/2 of its volume. So, effective number of atoms per unit cell = (1/8 *8) + (1/2*6) = 1+3 = 4.