(a) What is a close-packed array? Show with suitable diagrams the two possible variations? (3 marks) (b) With the aid of clear diagrams show what types of holes exist in close-packed arrays. (2 marks) (c) Sodium chloride has the rock salt structure. Explain how this relates to a close-packed array. What is the coordination geometry of each ion in NaCl? (3 marks) (d) Copy the two-dimensional grids shown below and on them clearly annotate the (1,0), (2,2) and (0,2) Miller indices, respectively. L (3 marks) (e) Draw unit cells of primitive and face-centred cubic crystal lattices and for each determine the number of lattice points per unit cell. (4 marks) (1) Draw the unit cell of a primitive orthorhombic crystal lattice. In