Q: Each of the following solids show, the Frenkel defect except

Explanation:

Frenkel Defect

A Frenkel defect is a type of point defect in a crystal structure where an ion, typically the smaller cation, leaves its regular position in the lattice and moves to an interstitial site. This creates a vacancy at the original site and an interstitial defect where the ion relocates. Frenkel defects are more common in ionic crystals where there is a significant size difference between the cations and anions, allowing the smaller ions to move more easily within the lattice.

Let’s examine each of the solids listed:

ZnS (Zinc Sulfide): ZnS has a structure where zinc ions (Zn²⁺) are relatively small compared to the sulfide ions (S²⁻). This size difference allows Zn²⁺ ions to migrate to interstitial sites, leading to the formation of Frenkel defects.

AgBr (Silver Bromide) and AgI (Silver Iodide): In both AgBr and AgI, silver ions (Ag⁺) are smaller and can move into interstitial positions within the crystal lattice. This mobility of Ag⁺ ions results in Frenkel defects, where vacancies and interstitials are created.

KCl (Potassium Chloride): Unlike the other solids mentioned, KCl has ions that are more similar in size (K⁺ and Cl⁻) and a crystal structure that does not favor the movement of potassium ions to interstitial sites. Instead of forming Frenkel defects, KCl primarily exhibits Schottky defects, where both potassium and chloride ions leave their lattice positions, creating vacancies without the formation of interstitials.

Therefore, among the options provided, KCl does not show Frenkel defects because its ionic structure and ion sizes do not support the formation of such defects.