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

Options

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

Answer

To determine which crystal does not exhibit a Frenkel defect, we need to understand what a Frenkel defect is and the conditions under which it occurs.

### Step-by-Step Solution:

1. **Understanding Frenkel Defect**:
- A Frenkel defect occurs when a cation (or an anion) leaves its lattice site and occupies an interstitial site. This defect is typically observed in ionic solids where there is a significant difference in the sizes of the cation and anion.

2. **Characteristics of Frenkel Defect**:
- It usually involves smaller cations moving to interstitial sites.
- The overall density of the crystal remains unchanged because only the position of the ions changes, not their number.

3. **Identifying the Options**:
- We need to analyze the given options to see which one does not exhibit a Frenkel defect. The options are:
- (a) Silver Bromide (AgBr)
- (b) Silver Chloride (AgCl)
- (c) Calcium Chloride (CaCl₂)
- (d) Zinc Sulfide (ZnS)

4. **Analyzing Each Option**:
- **Silver Bromide (AgBr)**:
- Ag⁺ is smaller than Br⁻, leading to a significant size difference. Thus, AgBr can exhibit a Frenkel defect.
- **Silver Chloride (AgCl)**:
- Similar to AgBr, Ag⁺ is smaller than Cl⁻, allowing for the possibility of a Frenkel defect.
- **Calcium Chloride (CaCl₂)**:
- In CaCl₂, the cation (Ca²⁺) and anions (Cl⁻) are of similar size. Typically, ionic solids with similar sizes of cations and anions do not exhibit Frenkel defects but rather Schottky defects, where equal numbers of cations and anions are missing from the lattice.
- **Zinc Sulfide (ZnS)**:
- Zn²⁺ is significantly smaller than S²⁻, so ZnS can also exhibit a Frenkel defect.

5. **Conclusion**:
- The crystal that does not exhibit a Frenkel defect is **Calcium Chloride (CaCl₂)**, as it typically exhibits Schottky defects instead.

### Final Answer:
**Calcium Chloride (CaCl₂)** does not exhibit a Frenkel defect.