In CsCl with cubic structure $Cl^-$ ions are located at each corner and $Cs^+$ ions at the centre of the unit cell. If $r_{Cs^+}$ and $r_{Cl^-}$ are $1.69A^{\large\circ}$ and $1.81A^{\large\circ}$ respectively . Find the value of edge length of cube.

Question

$(a)\;4\qquad(b)\;5\qquad(c)\;6\qquad(d)\;8$