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

There were 6A atoms on the face-centres. Removing face-centred 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  centres)                                                                                Number of B atoms per units cell =12×14(edge centred)+1              =4(body centred)  Hence the resultant stoichiometry is A3B4