The correct statement(s) regarding defects in solids is (are)

Options

A. Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion
B. Frankel defect is a diclocation defect
C. Traping of an electron in the lattice leads to the formation of F - centre
D. Schottky defects have no effect on the physical properties of solids

Answer

To solve the question regarding the correct statements about defects in solids, we will analyze each option provided and determine its validity based on our understanding of solid-state chemistry.

### Step-by-Step Solution:

1. **Understanding Frenkel Defect**:
- The Frenkel defect occurs when an ion (cation or anion) leaves its lattice site and occupies an interstitial site.
- This defect is typically favored when there is a **large difference in size** between the cation and anion.

**Evaluation of Statement 1**:
- The statement claims that the Frenkel defect is favored by a very small difference in size of cation and anion. This is **incorrect**.
- **Conclusion**: Statement 1 is false.

2. **Dislocation Effect in Frenkel Defect**:
- Since the Frenkel defect involves the movement of ions from their lattice positions to interstitial positions, it can indeed be described as a dislocation effect.

**Evaluation of Statement 2**:
- The statement claims that the Frenkel defect is a dislocation effect. This is **correct**.
- **Conclusion**: Statement 2 is true.

3. **Formation of F-Centers**:
- F-centers are formed when an electron occupies an anion vacancy in a crystal lattice. This typically occurs when an anion is missing, and the electron is trapped in that vacancy.

**Evaluation of Statement 3**:
- The statement claims that trapping of an electron in the lattice leads to the formation of F-centers. This is **correct**.
- **Conclusion**: Statement 3 is true.

4. **Schottky Defect and Physical Properties**:
- The Schottky defect involves the removal of equal numbers of cations and anions from the lattice, which results in a decrease in the total mass of the solid and consequently affects its density.

**Evaluation of Statement 4**:
- The statement claims that the Schottky defect has no effect on physical properties. This is **incorrect** because the defect does affect the density and other physical properties of the solid.
- **Conclusion**: Statement 4 is false.

### Final Conclusion:
The correct statements regarding defects in solids are:
- Statement 2: The Frenkel defect is a dislocation effect.
- Statement 3: Trapping of an electron in the lattice leads to the formation of F-centers.