Q.What type of stoichiometric defect is shown by:

• $ZnS$ — large size difference between $Zn^{2+}$ and $S^{2-}$ and low coordination number $\Rightarrow$ Frenkel defect. …

Step 1 – $ZnS$.

The cation $Zn^{2+}$ is much smaller than the anion $S^{2-}$, and the coordination number is low. Under these conditions the small cation is displaced into an interstitial site, so $ZnS$ shows the Frenkel defect (a dislocation defect).

Step 2 – $AgBr$. …

Match each solid to its stoichiometric defect using ionic-size difference and coordination number: large size difference/low CN $\to$ Frenkel ($ZnS$); …

• Giving only Frenkel for $AgBr$; it uniquely shows both Frenkel and Schottky.
• Assigning Schottky to $ZnS$; its large ionic-size difference favours Frenkel. …