(a) Portion of an atom at comer: An atom at corner is shared by eight adjacent unit cell. Four unit cells on one layer while four unit cells either above or below the layer, Hence, the portion of the atom at the comer that belongs to one unit cell is equal to 1/8.
(b) Portion of an atom at body centre: An atom at the centre of body of a cubic unit cell is not shared by any other unit cell. Hence, it belongs the whole part or fully to the unit cell.
