An ionic compound AB has ZnS type of structure if the radius of A⁺ is 22.5 pm, then the ideal radius of  B^- is

Since ionic compound AB has ZnS type of structure with co-ordination number 4;4.

F or co-ordination number 4 the radius ratio should range between 0.22 to 0.41.

$\frac{\mathrm{radius} \mathrm{of} \mathrm{cation}}{\mathrm{radius} \mathrm{of} \mathrm{anion}}=0.225$

$\begin{array}{l}\frac{{\mathrm{r}}_{+}}{{\mathrm{r}}_{-}}=0.225\\ \frac{22.5}{{\mathrm{r}}_{-}}=0.225\end{array}$

Hence, ${\mathrm{r}}_{-}=100\mathrm{pm}$