Question

Which one of the following crystals does not exhibit Frenkel defect
A) AgBr
B) AgCl
C) KBr
D) ZnS

Answer 1

Hint: To undergo Frankel defect the salt must have a large size difference between the corresponding ions. As the smaller cation will go to the interstitial site of the crystal and give rise to this defect.

Complete Step by Step Answer:
When a cation or anion leaves its site and occupies the interstitial position of a crystal lattice then the defect arises is called Frenkel defect.

The major characteristics of the Frenkel defect are:
- In this defect there is a very large difference in size between cation and anion.
- In this defect either cation or anion leave the solid crystal.
- Atoms or the ions do not move out of the crystal permanently in this defect.
- Here generally one vacancy is formed.
- The density of the solid remains the same.
Thus silver chloride, silver bromide and zinc sulphide have large size differences between the ions. So, these crystals show the Frenkel defect.

Again in potassium bromide the size of potassium ion and bromide ion is similar. So, it shows a schottky defect.
Thus the correct option is C.

Note: Generally the salt of alkali metals shows Schottky defect. Like sodium chloride, potassium bromide shows Schottky defect. Again the salt of transition metals shows the Frankel defect. Like zinc sulphide shows the Frankel defect.