Which of the following point defects are shown by AgBr (s) crystals ?
(a) Schottky defect
(b) Frenkel defect
( c) metal ecxess defect
(d) Metal deficiency defect

Options

A. (I) and (II)
B. (II) and (IV)
C. (I) and (III)
D. (II) and (IV)

Explanation

To determine which point defects are shown by AgBr (silver bromide) crystals, let's analyze the options provided.

### Step-by-Step Solution:

1. **Understanding Point Defects**:
- Point defects in crystals are irregularities that occur at specific points in the crystal lattice. The main types include Schottky defects, Frenkel defects, metal excess defects, and metal deficiency defects.

2. **Schottky Defect**:
- A Schottky defect occurs when an equal number of cations and anions are missing from the lattice, creating vacancies. In the case of AgBr, if both Ag⁺ and Br⁻ ions are missing from their lattice sites, this results in a Schottky defect.

3. **Frenkel Defect**:
- A Frenkel defect occurs when an ion (usually a cation) leaves its lattice site and occupies an interstitial site. In AgBr, if an Ag⁺ ion moves from its lattice position to an interstitial site, this creates a Frenkel defect.

4. **Metal Excess Defect**:
- A metal excess defect typically occurs when there are extra metal ions in the lattice, often due to the presence of anion vacancies. This is not characteristic of AgBr, as it does not have excess metal ions in its structure.

5. **Metal Deficiency Defect**:
- A metal deficiency defect occurs when there are fewer metal ions than expected in the lattice. This is also not a typical defect for AgBr.

6. **Conclusion**:
- Based on the analysis, AgBr crystals exhibit both Schottky and Frenkel defects. Therefore, the correct answer is option (a), which includes both types of defects.

### Final Answer:
AgBr (s) crystals show both Schottky and Frenkel defects. Thus, the correct option is (a).

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