Question

The correct example of ‘Frenkel Defect’ is:
A) ${\text{NaCl}}$
B) ${\text{CsCl}}$
C) ${\text{KCl}}$
D) ${\text{AgCl}}$

Answer 1

To solve this we must know that the irregularities formed in the arrangement of constituent particles are known as defects. Frenkel defect occurs when there is no disturbance in the stoichiometry of the solid. Frenkel defect occurs in ionic solids in which there is a large difference in the size of the ions.

Complete step-by-step answer:
We are given four ionic solids ${\text{NaCl}}$, ${\text{CsCl}}$, ${\text{KCl}}$ and ${\text{AgCl}}$. In these solids, the chloride anion i.e. ${\text{C}}{{\text{l}}^ - }$ is the same. The only difference is the cations. We know that the Frenkel defect occurs in ionic solids in which there is a large difference in the size of the ions. Thus, for the ionic solid to show Frenkel defect the difference in the size of cations and the chloride anion i.e. ${\text{C}}{{\text{l}}^ - }$ must be large.

The Frenkel defect occurs when the smaller atom or ion (usually cation) leaves its original place in the crystal lattice and creates a vacancy in the crystal lattice. The cation occupies another interstitial position in the crystal lattice. The density does not change when a Frenkel defect occurs. The ${\text{A}}{{\text{g}}^ + }$ cation in ${\text{AgCl}}$ solid is very small in size compared to the size of cations in ${\text{NaCl}}$, ${\text{CsCl}}$ and ${\text{KCl}}$.

Thus, the correct option is (D) ${\text{AgCl}}$.

Note: The defects arise when an atom or ion goes missing or dislocates from the crystal lattice or any atom gets added to the crystal lattice. Frenkel defect is a stoichiometric defect. In stoichiometric defects, the ratio of cations and anions does not change. Thus, the density does not change.