in which of the following strutures corrding number for cations and anions in the packed structure will be same ?

Options

A. `Cl^(-)` ions form fcc lattice and `Na^(+)` ions occupy all octahedral voids of the unit cell
B. `Ca^(2+)` ions form fcc lattice and `F^(-)` ions occupy all the eight tetrahedral voids of the unit cell
C. `O^(2-)` ions form fcc lattice and `Na^(+)` ions occupy all the eight tetrahedral voids of the unit cell
D. `S^(2-)` ions form fcc lattice and `Zn^(2+)` ions go into go into alternate tetrahedral voids of the unit cell

Explanation

To determine in which of the following structures the coordination number for cations and anions in the packed structure will be the same, we need to analyze each option carefully.

### Step-by-Step Solution:

1. **Understanding Coordination Number**:
- The coordination number is the number of nearest neighbors surrounding a central atom in a crystal structure. For ionic compounds, it refers to how many oppositely charged ions surround a given ion.

2. **Analyzing Option A: NaCl**:
- In NaCl, sodium ions (Na⁺) and chloride ions (Cl⁻) are arranged in a face-centered cubic (FCC) lattice.
- Each Na⁺ ion is surrounded by 6 Cl⁻ ions and vice versa.
- Therefore, the coordination number for Na⁺ is 6 and for Cl⁻ is also 6.
- **Conclusion**: Coordination numbers are the same.

3. **Analyzing Option B: CaF₂**:
- In CaF₂, calcium ions (Ca²⁺) occupy the FCC lattice, while fluoride ions (F⁻) occupy the tetrahedral voids.
- Each Ca²⁺ ion is surrounded by 8 F⁻ ions, but each F⁻ ion is surrounded by only 4 Ca²⁺ ions.
- **Conclusion**: Coordination numbers are not the same.

4. **Analyzing Option C: Na₂O**:
- In Na₂O, oxide ions (O²⁻) are in an FCC lattice, and sodium ions (Na⁺) occupy the tetrahedral voids.
- Each O²⁻ ion is surrounded by 4 Na⁺ ions, but each Na⁺ ion is surrounded by 4 O²⁻ ions.
- **Conclusion**: Coordination numbers are not the same.

5. **Analyzing Option D: ZnS**:
- In ZnS, zinc ions (Zn²⁺) occupy the FCC lattice, while sulfide ions (S²⁻) occupy the tetrahedral voids.
- Each Zn²⁺ ion is surrounded by 4 S²⁻ ions, and each S²⁻ ion is surrounded by 4 Zn²⁺ ions.
- **Conclusion**: Coordination numbers are the same.

6. **Final Answer**:
- The structures where the coordination number for cations and anions is the same are:
- Option A: NaCl
- Option D: ZnS

### Summary:
The correct options where the coordination number for cations and anions is the same are A (NaCl) and D (ZnS).