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” = $\left(4\times \frac{1}{2}\right)+8\left(\frac{1}{8}\right)=3$

Number of effectiive atoms of “B” = $12\times \frac{1}{4}=3$

Formula of the compound =A₃B₃=AB