In the Schottky defect

Options

A. cations are missing from the lattice sites and occupy the interstitial sites
B. equal number of cations and anions are missing
C. anions are missing and electrons are present in their place
D. equal number of extra cations and electrons are present in the interstitial sites

Answer

**Step-by-Step Solution:**

1. **Understanding Schottky Defect**:
- The Schottky defect is a type of point defect in ionic solids, where equal numbers of cations and anions are missing from their lattice sites. This defect maintains the electrical neutrality of the crystal.

2. **Analyzing the Options**:
- **Option A**: Cations are missing from lattice sites and occupy interstitial sites.
- This describes the Frenkel defect, not the Schottky defect.
- **Option B**: Equal number of cations and anions are missing.
- This is correct as it describes the Schottky defect accurately.
- **Option C**: Anions are missing and electrons are present in their place.
- This describes anionic vacancies, which is not a characteristic of the Schottky defect.
- **Option D**: Equal number of extra cations and electrons are present in interstitial sites.
- This describes a metal excess defect, which is also not related to the Schottky defect.

3. **Conclusion**:
- The only correct option that describes the Schottky defect is **Option B**, which states that equal numbers of cations and anions are missing from the lattice.

**Final Answer**: B) Equal number of cations and anions are missing.

---