Defects in crystal Questions in English

(C) Frenkel defect is observed in ionic crystals where there is a large difference in the size of the ions. Specifically, it occurs when the smaller ion (usually the cation) leaves its lattice site and occupies an interstitial site.
$AgCl$ exhibits Frenkel defect because the $Ag^+$ ion is significantly smaller than the $Cl^-$ ion, allowing it to move into an interstitial position.
$NaCl$, $KCl$, and $CsCl$ typically exhibit Schottky defect due to the similar sizes of their constituent ions.