A compound is formed by cation C and anion A. The anions form hexagonal close packed (hcp) lattice and the cations occupy 75% of octahedral voids. The formula of the compound is

Number of atoms per unit cell in hcp = 6Number of octahedral void in hcp = 6Number of anions per unit cell(A) = 6Number of octahedral voids occupied by cations(C) = 6×75100=92∴    Formula of compound = C3A4