JEE Main · 2023 · 15 Apr 2023 · Shift 1 · Solid State

In the CsCl unit cell, Cs⁺ is present at the body center and Cl⁻ ions are at all eight corners. The ions touch along the body diagonal of the cube. The body diagonal length is $\sqrt{3}a$, where $a$ is the edge length. Since the body diagonal contains one Cs⁺ radius and one Cl⁻ radius on each side of the center, we have: ${\mathrm{r}}_{{\mathrm{Cs}}^{+}}+{\mathrm{r}}_{{\mathrm{Cl}}^{-}}=\frac{\sqrt{3}a}{2}$.