Question

In a cubic crystal anions are arranged in fcc and the cations occupy half the tetrahedral voids and all the octahedral voids. The ratio of cations and anions in the crystal is

Answer 1

In a close packing, the number of octahedral voids is equal to the number of atoms and the number of tetrahedral voids is twice the number of atoms Since all the octahedral voids and half the tetrahedral voids are filled there will be one atom of B in tetrahedral void and one atom in octahedral void corresponding to each A. Thus, there will be two atoms of B corresponding to each A.

Hence, formula of the solid is AB2