A tetrad axis is the line passing through opposite face centers and a body center. AB has rock salt structure. If all the particles along a tetrad axis are removed then formula of the compound will be

Particles are removed from two face centres and a body centre."A" atoms form ccp and “B” atoms occupy all the octahedral voids.Number of effective atoms of “A” = 4×12+818=3Number of effectiive atoms of “B” = 12×14=3Formula of the compound =A3B3=AB