Element ‘B’ cystallizes to ccp arrangement and ‘A’ occupies half of octahedral voids while oxygen atoms occupy all the tetrahedral voids. The formula of the compound is

If ‘N’ atoms are forming lattice then 2N tetrahedral voids and N octahedral voids are formed.In ccp structure , Number of atoms of B=4 Number of atoms of A =12×(Octahedral voids)   =42=2 Number of O-atoms =2(4)=8 A:B:O = 2:4:8 =1:2:4 The formula of the compoud is AB2O4