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?

73) A compound alloy of gold and copper crystallizes in a cube lattice in which the gold atoms occupy the lattice points at the corners of cube and copper atoms occupy the centers of each of the cube faces. The formula of this compound is: