In a solid 'AB' having the NaCl structure, 'A' atoms occupy the corners of the cubic unit cell. If all the face centered atoms along one of the axes are removed, then the resultant stoichiometry of the solid will be

There were 6A. atoms on the face-centers removing face-centered atoms along one of the axes means removal of 2A atoms.Now, number of A atoms per unit cell =8×18     +  4×12=3 (corners) (face-centred) Number of B atoms per unit cell 1=12×14       +          1=4 (edgecentred)   (bodycentred)  Hence the resultant stoichiometry is A3B4.