Question

Ionic radii of cation A+ and anion B- are 102 and 181 pm, respectively. These ions are allowed to crystallize into an ionic solid. This crystal has cubic close packing for B-. A+ is present in all octahedral voids. The edge length of the unit cell of the crystal AB is _____pm. (Nearest integer)

Answer 1

In cubic close packing, octahedral voids form at edge centers and body center of the cube
a =$2(r_A^+ + r_B^-)$
a = 2 (102 + 181)
a = 566 pm
So, the answer is 566 pm.