The `Ca^(2+)` and `F^(-)` ions arc located in `CaF_(2)` crystal respectively at face centred cubic lattice points and in

Options

A. tetrahedral voids
B. half of tetrahedral voids
C. octahedral voids
D. half of octahedral voids.

Explanation

To solve the question regarding the arrangement of `Ca^(2+)` and `F^(-)` ions in the `CaF_(2)` crystal structure, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Crystal Structure**:
- Calcium fluoride (CaF2) has a face-centered cubic (FCC) lattice structure for the `Ca^(2+)` ions.
- In this structure, `Ca^(2+)` ions occupy the corners and the centers of the faces of the cubic unit cell.

2. **Identifying the Position of `F^(-)` Ions**:
- The `F^(-)` ions occupy the tetrahedral voids in the FCC lattice formed by the `Ca^(2+)` ions.
- Tetrahedral voids are formed when four `Ca^(2+)` ions surround a central void.

3. **Coordination Numbers**:
- The coordination number for `Ca^(2+)` ions in this structure is 8, meaning each `Ca^(2+)` ion is surrounded by 8 `F^(-)` ions.
- Conversely, the coordination number for `F^(-)` ions is 4, indicating that each `F^(-)` ion is surrounded by 4 `Ca^(2+)` ions.

4. **Conclusion**:
- In summary, in the `CaF_(2)` crystal, `Ca^(2+)` ions are located at the face-centered cubic lattice points, while `F^(-)` ions occupy all tetrahedral voids.
- Therefore, the correct answer is that `Ca^(2+)` ions are at face-centered cubic lattice points and `F^(-)` ions are in tetrahedral voids.

### Final Answer:
The `Ca^(2+)` ions are located at face-centered cubic lattice points, and the `F^(-)` ions are located in tetrahedral voids.

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