65) Anion A²⁻ forms cubic close packing and cation B²⁺ occupies 25% octahedral holes, while cation B³⁺ occupies equal number of tetrahedral and octahedral holes. If number of octahedral holes occupied by B²⁺ and B³⁺ are equal, then formula of the molecule is:

66) An ionic solid M₂X₃ has a cubic unit cell. Which of the following arrangements of the ions is consistent with the stoichiometry of the compound?

67) AB crystallizes in a body centered cubic lattice with edge length, a = 387 pm. The distance between two oppositely charged ions in the lattice is:

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: