Which of the following statements regarding defects in crystalline solids is correct?

Options

A. Schottky defects have no effect on the density of crystalline solides
B. Frenkel defects decreases the density of crystalline solides
C. Frenkel defects is a dislocation defect
D. Frenkel defect is found in halides of alkaline metals

Explanation

To determine which statement regarding defects in crystalline solids is correct, we need to analyze the definitions and characteristics of Schottky and Frenkel defects.

### Step-by-Step Solution:

1. **Understanding Schottky Defect**:
- A Schottky defect occurs when equal numbers of cations and anions are missing from their lattice sites in a crystalline solid. This results in vacancies that reduce the overall density of the solid.
- **Example**: Common examples of materials exhibiting Schottky defects include NaCl, KCl, and AgBr.

2. **Understanding Frenkel Defect**:
- A Frenkel defect occurs when a cation leaves its lattice site and occupies an interstitial site (a void) within the crystal structure. This defect does not change the overall density of the crystal because the number of ions remains the same, just their positions change.
- **Example**: Examples of materials with Frenkel defects include Zinc Sulphide (ZnS) and Silver Chloride (AgCl).

3. **Evaluating the Statements**:
- **Statement 1**: "Schottky defect has no effect on the density of crystalline solids."
- This is incorrect because Schottky defects decrease the density.

- **Statement 2**: "Frenkel defects decrease the density of crystalline solids."
- This is also incorrect because Frenkel defects do not affect the density.

- **Statement 3**: "Frenkel defects is a dislocation defect."
- This is correct. A Frenkel defect involves the displacement of a cation from its lattice site to an interstitial site, which is indeed a type of dislocation defect.

- **Statement 4**: "Frenkel defects are found in halides of alkaline metals."
- This is incorrect. Frenkel defects are not typically found in halides of alkaline metals; they are more commonly found in compounds like ZnS and AgCl.

4. **Conclusion**:
- The only correct statement among the options provided is the third one: "Frenkel defects is a dislocation defect."

### Final Answer:
The correct statement regarding defects in crystalline solids is: **"Frenkel defects is a dislocation defect."**