The structure of an ionic compound${\mathrm{x}}^{+}{\mathrm{y}}^{-}$  has ZnS type structure. If radius of x⁺ is 100 pm, calculate the ideal radius of Y^-. If radius of ${\mathrm{x}}^{+}$  is enlarged by some special

 technique to 184 pm, in which type of the structure would$\mathrm{xy}$ and also determine its co-ordination number? 

For ZnS type crystal, consider the radius ratio of tetrahedral void, which is 0.225

For the given type of compound :  

     $\begin{array}{l}\begin{array}{ccc}\frac{{\mathrm{r}}^{+}}{{\mathrm{r}}^{-}}& =& 0.225\\ \frac{100 \mathrm{pm}}{{\mathrm{r}}^{-}}& =& 0.225\\ {\mathrm{r}}^{-}& =& 444.44 \mathrm{pm}\end{array}\end{array}$

New radius after the value of ${\mathrm{x}}^{-}$ becomes 184 pm

     $\frac{{\mathrm{r}}^{+}}{{\mathrm{r}}^{-}}=\frac{184 \mathrm{pm}}{444.44 \mathrm{pm}}=0.4$

xy becomes $\mathrm{NaCl}$ type structure and co-ordination number becomes 6.