In a face centered cubic arrangement of A and B atoms in which ‘A’ atoms are at the corners of the unit cell and ‘B’ atoms are at the face centers. One of the ‘A’ atom is missing from one corner in unit cell. The simplest formula of compound is

Number of effective A atoms =7 corners X 1/8 X per corner atom share ( since one atom missing from one corner)                                               = 78ANumber of effective B atoms = 6 faces X 12per face atom share = 3BFormula of FCC unit cell =A78B3 =A7B24