The anionic sites occupied by electrons are called

Options

A. X-center
B. Y-center
C. S-center
D. F-center

Answer

To solve the question regarding the anionic sites occupied by electrons, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify what the anionic sites occupied by electrons are called in solid-state chemistry.

2. **Identifying the Context**: The question relates to defects in ionic crystals, specifically metal excess defects. In these defects, there are anionic vacancies created when cations are added to the crystal lattice.

3. **Example of Sodium Chloride**: Consider sodium chloride (NaCl) as an example. In its crystal structure, sodium ions (Na⁺) are cations and chloride ions (Cl⁻) are anions.

4. **Heating the Crystal**: When the NaCl crystal is heated in the presence of sodium vapor, sodium atoms get deposited on the surface. This causes some chloride ions to leave their lattice positions, creating an anionic vacancy.

5. **Electron Occupation**: The sodium atoms that lose their electrons become Na⁺ ions. The electrons that are freed occupy the vacant anionic sites left by the chloride ions.

6. **Naming the Anionic Sites**: The specific sites where these electrons occupy the anionic vacancies are referred to as "F centers."

7. **Conclusion**: Based on the understanding and the example provided, the answer to the question is that the anionic sites occupied by electrons are called **F Centers**.

### Final Answer:
The anionic sites occupied by electrons are called **F Center**.

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