Which one of the following crystal does not exhibit Frenkel defect?

Options

A. AgBr
B. AgCl
C. KBr
D. ZnS

Answer

To determine which crystal does not exhibit a Frenkel defect, we need to understand the characteristics of Frenkel and Schottky defects in ionic crystals.

### Step-by-Step Solution:

1. **Understanding Frenkel Defect**:
- A Frenkel defect occurs when a cation leaves its lattice site and occupies an interstitial site. This defect typically arises when there is a significant size difference between cations and anions.
- The two main conditions for a Frenkel defect are:
- There is a large difference in the size of cations and anions.
- The coordination number is low.

2. **Identifying Examples of Frenkel Defect**:
- Common examples of crystals that exhibit Frenkel defects include:
- Silver bromide (AgBr)
- Silver chloride (AgCl)
- Zinc sulfide (ZnS)

3. **Understanding Schottky Defect**:
- A Schottky defect occurs when both a cation and an anion are missing from their lattice sites, maintaining overall charge neutrality. This defect is typically found in crystals where the sizes of cations and anions are similar.
- The conditions for a Schottky defect are:
- Cations and anions are of almost similar size.
- The coordination number is high.

4. **Identifying Examples of Schottky Defect**:
- Common examples of crystals that exhibit Schottky defects include:
- Sodium chloride (NaCl)
- Potassium bromide (KBr)
- Silver bromide (AgBr) can exhibit both defects depending on conditions.

5. **Analyzing the Options**:
- The question asks for a crystal that does not exhibit a Frenkel defect. Based on the examples provided:
- Potassium bromide (KBr) is identified as an example of a Schottky defect, not a Frenkel defect.

6. **Conclusion**:
- Therefore, the crystal that does not exhibit a Frenkel defect is **Potassium Bromide (KBr)**.

### Final Answer:
**Potassium Bromide (KBr)** does not exhibit a Frenkel defect.