Frenkel defect is commonly noticed in:

Options

A. AgBr
B. ZnS
C. AgI
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Frenkel Defect**:
- A Frenkel defect occurs when a cation leaves its normal lattice position and occupies an interstitial site within the crystal lattice. This results in a vacancy at the original position of the cation.

2. **Characteristics of Frenkel Defect**:
- It is commonly found in ionic compounds.
- It typically occurs in compounds where the cation is significantly smaller than the anion.
- The cation's smaller size allows it to fit into the interstitial sites of the lattice.

3. **Examples of Compounds with Frenkel Defect**:
- Common examples include:
- Silver bromide (AgBr)
- Zinc sulfide (ZnS)
- Silver iodide (AgI)
- In these compounds, the anions (Br⁻, I⁻, S²⁻) are larger than the cations (Ag⁺, Zn²⁺), which facilitates the occurrence of the Frenkel defect.

4. **Reason for Occurrence**:
- The larger size of the anions creates more space in the lattice, allowing the smaller cations to migrate to interstitial sites, thereby creating vacancies.

5. **Coordination Number**:
- Frenkel defects are more likely to occur in ionic compounds with low coordination numbers, where the arrangement of ions allows for such movement.

### Conclusion:
Frenkel defects are commonly noticed in ionic compounds where the cation is smaller than the anion, such as AgBr, ZnS, and AgI.

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