In a crystalline solid anions B are arranged in cubic close packing. Cation A are equally distributed between octahedral and tetrahedral voids. If all the octahedral voids are occupied, the formula for the solid is

Explanation

Suppose the number of anions B = n. Then number of octahedral voids = n .
Number of tetrahedral voids = 2n.
As octahedral and tetradhedral voids are equally occupied by cations A and all the octahedral voids are occupied (given) therefore, n capitan A are present in octahedral voids and n cations A are present in tetrahedral voids. In other words, correshponding to n anions B , there are n +n = 2n cations A. Thus, A and anuions B are in the ratio 2n: n =2 : 1 hence, the formual of the solid will be `A_(2) B` .