The correct statement regarding defects in crystalling solids.

Options

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

Answer

To solve the question regarding the correct statement about defects in crystalline solids, we need to analyze the definitions and characteristics of two types of defects: Frenkel defect and Schottky defect.

### Step-by-Step Solution:

1. **Understanding Frenkel Defect**:
- In a Frenkel defect, a cation is displaced from its original lattice position to an interstitial site. This creates a vacancy where the cation was originally located.
- The important point is that the cation remains in the crystal structure, just in a different position.
- This defect does not change the overall density of the solid because the total number of ions remains the same.

2. **Understanding Schottky Defect**:
- In a Schottky defect, an equal number of cations and anions are missing from the crystal lattice.
- This results in a decrease in the density of the solid because there are fewer ions present in the lattice structure.

3. **Analyzing the Statements**:
- **Statement 1**: "Frenkel defect is a dislocation defect."
- This is correct because it describes the nature of the Frenkel defect accurately.
- **Statement 2**: "Frenkel defect is found in halides of alkaline earth metals."
- This is incorrect. Frenkel defects occur in ionic solids with a significant size difference between cations and anions, not limited to alkaline earth metal halides.
- **Statement 3**: "Schottky defect has no effect on the density of crystalline solid."
- This is incorrect because the Schottky defect decreases the density due to missing ions.
- **Statement 4**: "Frenkel defect decreases the density of crystal solid."
- This is also incorrect as the density remains unchanged in a Frenkel defect.

4. **Conclusion**:
- The only correct statement regarding defects in crystalline solids is Statement 1: "Frenkel defect is a dislocation defect."

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