Which of the follwing statements is/are correct for both fluorite and antifluorite structures?

Options

A. Cation is present in alternate `TV_(s)`
B. Anion constitutes lattice.
C. Number of formula unit in one unit cell is `4`.
D. `100%` tetrahedral voids are occupied

Explanation

To determine which statements are correct for both fluorite and antifluorite structures, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Fluorite Structure**:
- In the fluorite structure (e.g., CaF2), the cations (Ca²⁺) form a face-centered cubic (FCC) lattice, while the anions (F⁻) occupy the tetrahedral voids.
- In this structure, there are 4 formula units of CaF2 per unit cell.

2. **Understanding Antifluorite Structure**:
- In the antifluorite structure (e.g., Na2O), the anions (O²⁻) form a face-centered cubic (FCC) lattice, while the cations (Na⁺) occupy the tetrahedral voids.
- Similar to the fluorite structure, there are also 4 formula units of Na2O per unit cell.

3. **Analyzing Each Statement**:
- **Option A**: "Cation is present in alternate tetrahedral voids."
- This is incorrect for both structures. In fluorite, cations are in the lattice, while in antifluorite, cations occupy tetrahedral voids but not in an alternate manner.

- **Option B**: "Anion constitutes lattice."
- This is only true for antifluorite, where the anions form the lattice. In fluorite, the cations form the lattice. Therefore, this statement is incorrect for both structures.

- **Option C**: "Number of formula units in one unit cell is 4."
- This statement is correct for both structures. Both fluorite and antifluorite have 4 formula units per unit cell.

- **Option D**: "100% tetrahedral voids are occupied."
- This statement is also correct. In fluorite, all tetrahedral voids are occupied by anions, and in antifluorite, all tetrahedral voids are occupied by cations.

4. **Conclusion**:
- The correct statements for both fluorite and antifluorite structures are **Option C** and **Option D**.

### Final Answer:
The correct statements for both fluorite and antifluorite structures are **C and D**.