Which of the following statements are correct in context of point defects in a crystal?

Options

A. AgCl has anion Frenkel defect and `CaF_(2)` has Schottky defects
B. AgCl has cation Frenkel defects and `CaF_(2)` has anion Frenkel defects
C. AgCl as well as `CaF_(2)` have anion Frenkel defects
D. AgCl as well as `CaF_(2)` has Schottky defects

Answer

To determine which statements are correct regarding point defects in crystals, we will analyze each statement based on the definitions and characteristics of Schottky and Frenkel defects.

### Step-by-Step Solution:

1. **Understand Point Defects**:
- Point defects are imperfections in a crystal lattice that occur at a single lattice point. The two main types of point defects are Schottky defects and Frenkel defects.

2. **Schottky Defect**:
- In a Schottky defect, an equal number of cations and anions are missing from their lattice sites. This leads to a decrease in the density of the crystal. Schottky defects are typically observed in ionic compounds like NaCl, KCl, and KBr.

3. **Frenkel Defect**:
- In a Frenkel defect, a smaller ion (usually a cation) leaves its lattice position and occupies an interstitial site. This defect does not change the overall stoichiometry of the compound but can affect its properties. Frenkel defects are commonly found in compounds like AgCl and CaF2.

4. **Analyze Each Statement**:
- **Statement 1**: "AgCl has anion Frenkel defect and calcium fluoride has Schottky defect."
- **Analysis**: This is incorrect. AgCl has a cation Frenkel defect (Ag+ is smaller and occupies interstitial sites), and CaF2 has an anion Frenkel defect (F- is smaller and occupies interstitial sites).

- **Statement 2**: "AgCl has cation Frenkel defect and calcium fluoride has anion Frenkel defect."
- **Analysis**: This is correct. Ag+ is the smaller cation in AgCl, and F- is the smaller anion in CaF2, leading to cation and anion Frenkel defects, respectively.

- **Statement 3**: "AgCl as well as calcium fluoride has anion Frenkel defect."
- **Analysis**: This is incorrect. Only CaF2 has an anion Frenkel defect; AgCl has a cation Frenkel defect.

- **Statement 4**: "AgCl as well as calcium fluoride has Schottky defects."
- **Analysis**: This is also incorrect. Both AgCl and CaF2 are characterized by Frenkel defects, not Schottky defects.

5. **Conclusion**:
- The only correct statement is **Statement 2**: "AgCl has cation Frenkel defect and calcium fluoride has anion Frenkel defect."

### Final Answer:
The correct statement in the context of point defects in a crystal is **Statement 2**.

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