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:

89) KF has NaCl sructure with edge length 537.5 x 10⁻¹² m. What is the distance between K⁺ and F⁻ in KF, if density is 2.48 gm⁄cc?

90) An alloy of Cu, Ag and Au is found to have copper constituting ccp lattice. If silver atoms occupy the edge centers and gold is present at body centers, the alloy has the formula:

91) In a cubic packed structure of mixed oxides, the lattice is made up of oxide, one fifth of tetrahedral voids are occupied by divalent ions (A²⁺), while one half of the octahedral voids are occupied by trivalent ions (B³⁺), then the formula of the oxide is: