An elemental crystal with a cubic structure has a lattice constant of a and, therein, each atom has a coordination number of 6 (see unit cell below). For each of its (100), (110), and (111) planes, determine (a) number of broken bonds for each atom on the plane, (b) number of atoms per unit area of the plane, and (c) specific surface energy of the plane with the use of =21N2a (20 marks)