Tetrahedral and octahedral holes are formed by the vacancies left when anions pack in a ccp array.

(a) Which hole can accommodate the larger ions?

(b) What is the radius ratio of the largest metal cation that can occupy an octahedral hole to the largest that can occupy a tetrahedral hole while maintaining the closepacked nature of the anion lattice?

(c) If half the tetrahedral holes are occupied, what is the empirical formula of the compound M_xA_y, where M represents the cations and A the anions?