68) Fraction of total volume occupied by atoms in a simple cube is:

69) In a crystal, both ions are missing from normal sites in equal number. This is an example of:

70) Xenon crystallizes in fcc lattice and the edge of the unit cell is 620 pm, then the radius of Xe atom is:

71) The edge length of cube is 400 pm. Its body diagonal would be:

72) What is the simplest formula of a solid whose cubic unit cell has the atom A at each corner, the atom B at each face center and atom C at the body center?