Question

The CsCl type structure is exhibited by alkali halides only when the radius of the cation is large enough to keep touching its eight nearest neighbour anions. Below what minimum ratio of cation to anion radii $\left(\frac{r_{+}}{r_{-}}\right)$ this contact is prevented ?

• A. 0.225
• B. 0.414
• C. 0.632
• D. 0.732

Answer 1

The correct option is D

0.732

CsCl is a 8 : 8 coordination compound i.e., $C{s}^{+}$ ion occupies a cubic hole of $C{l}^{-}$ ions packing. For exact fitting of cubic hole, the radii ratio $\frac{r_{+}}{r_{-}}$ must be 0.732.