Explain how many portions of an atom located at (i) corner and (ii) body-center of a cubic unit cell is part of its neighbouring unit cell.

The portion of an atom of the corner of a cubic unit cell is shared by eight adjacent unit cells as shown below:

Therefore, a portion of the atom at the corner = 8 × 1/8 = 1 atom.

(ii) The atoms present at the center of the body is not shared by its neighbouring unit cell.

Therefore, portion of the atom at the center = 1 atom