Solution:
AB is just like NaCl. Thus twelve A+ are at edges and 1 with in body of fcc i.e. in octahedral voids and six B- at faces and 8 at corner.
For fcc if AB is just like the rock salt like structure then, A+ and B- are located at
AB is just like NaCl. Thus twelve A+ are at edges and 1 with in body of fcc i.e. in octahedral voids and six B- at faces and 8 at corner.