(a) Why does the old glass object appear slightly milky instead of being transparent? (b) What do you meant by unit cell of crystal lattice?

What do you understand by unit cell of a crystal?

(a) An element crystallises in a cubic crystal structure with unit cell's edge length of 3.15Å. The atomic mass and the density of the element are 96 amu and 10.2g*cm^(-3) . Predict the crystal lattice possessed by the element. (b) What type of stoichiometric defects is shown by AgCl?

What do you mean by coordination number of a constituent particle in a crystal lattice? What are the coordination numbers in each of the close-packing of spheres: (a) square close-packing (b) hexagonal close-packing in two dimensions?