The coordination number of cation and anion in fluorite `CaF_(2)` and anti-fluroite `Na_(2)O` are respectively:

Options

A. 8:4 and 6:3
B. 6:3 and 4:4
C. 8:4 and 4:8
D. 4:8 and 8:4

Answer

To determine the coordination number of cation and anion in fluorite (CaF₂) and anti-fluorite (Na₂O), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Cation and Anion**:
- In **CaF₂**, the cation is **Ca²⁺** and the anion is **F⁻**.
- In **Na₂O**, the cation is **Na⁺** and the anion is **O²⁻**.

2. **Analyze the Structure of CaF₂ (Fluorite)**:
- The structure of CaF₂ is face-centered cubic (FCC) for the cation (Ca²⁺).
- In FCC, there are 4 cations (Ca²⁺) per unit cell (8 corner atoms contributing 1/8 each + 6 face-centered atoms contributing 1/2 each).

3. **Determine the Number of Tetrahedral Voids**:
- In a FCC structure, the number of tetrahedral voids is twice the number of cations.
- Therefore, for 4 Ca²⁺ ions, there are **8 tetrahedral voids**.

4. **Assign Anions to Tetrahedral Voids**:
- The F⁻ ions occupy all the tetrahedral voids.
- Thus, there are **8 F⁻ ions** in the structure.

5. **Calculate Coordination Numbers for CaF₂**:
- The coordination number of the cation (Ca²⁺) is the number of nearest F⁻ ions, which is **8**.
- The coordination number of the anion (F⁻) is the number of nearest Ca²⁺ ions, which is **4**.
- Therefore, the coordination numbers for CaF₂ are **8 (cation) : 4 (anion)**.

6. **Analyze the Structure of Na₂O (Anti-Fluorite)**:
- In Na₂O, the anion (O²⁻) is larger than the cation (Na⁺), leading to a different arrangement.
- The O²⁻ ions are arranged in a FCC structure, similar to Ca²⁺ in CaF₂.

7. **Determine the Number of Cations in Na₂O**:
- The number of O²⁻ ions in the FCC structure is **4**.
- The number of tetrahedral voids is again **8**.

8. **Assign Cations to Tetrahedral Voids**:
- The Na⁺ ions occupy all the tetrahedral voids.
- Thus, there are **8 Na⁺ ions** in the structure.

9. **Calculate Coordination Numbers for Na₂O**:
- The coordination number of the cation (Na⁺) is the number of nearest O²⁻ ions, which is **4**.
- The coordination number of the anion (O²⁻) is the number of nearest Na⁺ ions, which is **8**.
- Therefore, the coordination numbers for Na₂O are **4 (cation) : 8 (anion)**.

### Final Answer:
- The coordination numbers for CaF₂ (fluorite) are **8 (cation) : 4 (anion)**.
- The coordination numbers for Na₂O (anti-fluorite) are **4 (cation) : 8 (anion)**.