(i) The primitive unit cell consists of one atom at each of the 8 corners; each atom is thus shared by 8 unit cells. Hence n = 8 x (1/8) = 1
(ii) The b.c.c unit cell consists of 8 atoms at the 8 corners and one atom at the centre. At each corner only 1/8th of the atom is within the unit cell. Thus the contribution of the 8 corners is 8 x (1/8) = 1 while that of the body-centred atom is 1. Hence, n = 1+1 =2
(iii) The 8 atoms at the corners contribute 8 x (1/8) = 1 atom. There is one atom each of the 6 faces, which is shared by 2 unit cells each. Therefore, the contribution face-centred atoms = 6x (1/2) = 3 Hence, n = 1+3 = 4.
