State the difference between Schottky and Frenkel defects. Which of these two changes the density of the solid ?

Explanation

### Step-by-Step Solution:

1. **Definition of Schottky Defect**:
- A Schottky defect occurs when a pair of oppositely charged ions (cation and anion) leave the crystal lattice, creating vacancies. This results in a decrease in the density of the solid because the mass of the solid decreases while the volume increases due to the absence of these ions.

2. **Definition of Frenkel Defect**:
- A Frenkel defect occurs when a cation leaves its lattice site and occupies an interstitial site within the crystal structure. In this case, the overall mass of the solid remains the same, and the volume does not change significantly because the ion is still part of the solid, just relocated.

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