If the ionic radii of ${\mathrm{M}}^{+} \mathrm{and} {\mathrm{X}}^{-}$ are about 135 pm, then expected values of metallic radii of M and X should be respectively

The radius of cation is always smaller than${\mathrm{r}}_{\mathrm{M}}=230\mathrm{pm}; {\mathrm{r}}_{\mathrm{X}}=60 \mathrm{pm}$ the radius of parent atom. But the radius of anion is always larger than the radius of parent atom.

Metallic radii of $\mathrm{M}>{\mathrm{M}}^{+} \mathrm{and} \mathrm{ionic} \mathrm{radii} \mathrm{of} {\mathrm{X}}^{-}>\mathrm{X}$

Hence,