When electron are trapped into the crystal in anion cancy ,the defect is known as

Options

A. F-centre
B. Frenkel defect
C. Schottky defect
D. Interstitial defect

Explanation

To solve the question, we need to understand the concept of defects in crystal structures, particularly focusing on the scenario where electrons occupy vacancies in the crystal lattice.

### Step-by-Step Solution:

1. **Understanding Crystal Defects**:
- In solid-state chemistry, defects in crystals can occur due to missing atoms or ions, which can lead to vacancies. These defects can significantly affect the properties of the material.

**Hint**: Familiarize yourself with types of crystal defects, such as vacancies, interstitials, and substitutional defects.

2. **Identifying the Type of Defect**:
- The question specifically mentions "electrons trapped into the crystal in anion vacancy." This indicates that there is a missing anion (negatively charged ion) in the crystal lattice.

**Hint**: Recall that anion vacancies occur when an anion is missing from its lattice position, creating a vacancy.

3. **Understanding F Centers**:
- When an anion vacancy is created, it can be occupied by one or more electrons. These electrons are known as F centers (or color centers). F centers are responsible for the color of certain ionic crystals because they can absorb visible light.

**Hint**: Remember that F centers are specifically associated with anion vacancies filled by electrons.

4. **Conclusion**:
- Based on the understanding of F centers, we can conclude that when electrons are trapped in an anion vacancy within a crystal, the defect is referred to as an F center.

**Hint**: Connect the concept of F centers with their role in color absorption in crystals.

### Final Answer:
The defect is known as **F center**.