84) The ratio of cationic radius to anionic radius in an ionic crystal is greater than 0.732. Its coordination number is:

85) Na and Mg crystallize in bcc and fcc type crystals respectively. The number of atoms of Na and Mg present in the unit cell of their respective crystal is:

86) A solid is made up of 2 elements X and Z. The atoms Z are in ccp arrangement, while the atoms X occupy all the tetrahedral sites. What is the formula of the compound?

87) An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centers of the faces of the cube. The empirical formula for this compound would be:

88) A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of: