Ionic lattic has two major points defects ,(1) Schottky (2) Frenkel defects . Schottkly defects occurs due to the cations - anion pair's missing from the lattice sites . Frenkel defects occurs when cation leaves its lattice site and fits into an interstitial space. The neutrality of the crystal is being maintained and we considered all losses from interstitial positions.
which defect decrease density of the crystal ?

Options

A. Frenkel defect
B. Schootky defect
C. both (a) and (b)
D. None of these

Answer

To determine which defect decreases the density of the crystal between Schottky and Frenkel defects, we can analyze each defect step by step.

### Step-by-Step Solution:

1. **Understanding Schottky Defect**:
- In a Schottky defect, equal numbers of cations and anions are missing from their lattice sites.
- This means that there are vacancies created in the crystal structure where both cations and anions should be located.

2. **Effect on Crystal Density**:
- The removal of cations and anions leads to a decrease in the total mass of the crystal.
- Since density is defined as mass per unit volume, the loss of mass due to missing ions results in a decrease in the overall density of the crystal.

3. **Understanding Frenkel Defect**:
- In a Frenkel defect, a cation leaves its lattice site and occupies an interstitial site (a space between the lattice points).
- This means that while the cation is no longer in its original position, it is still present in the crystal structure.

4. **Effect on Crystal Density**:
- The total number of ions in the crystal remains the same because the cation that leaves its lattice site is still present in the crystal, just in a different location.
- Therefore, the mass of the crystal does not change, and the density remains constant.

5. **Conclusion**:
- Since the Schottky defect results in the loss of both cations and anions, it decreases the density of the crystal.
- In contrast, the Frenkel defect does not affect the total mass of the crystal, and thus the density remains unchanged.

**Final Answer**: The Schottky defect decreases the density of the crystal.