Solid State

In bcc - points are at corners and one in the center of the unit cell.

Number of atoms per unit cell $ = 8 \times {1 \over 8} + 1 = 2.$

In fcc - points are at the corners and also centre of the six faces of each cell.

Number of atoms per unit cell $ = 8 \times {1 \over 8} + 6 \times {1 \over 2} = 4.$