In which of the following structures coordination 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 `Fi^(-)` ons 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 alternate tetrahedral voids of the unit cell

Explanation

To determine in which of the given structures the coordination number for cations and anions in the packed structure is the same, we will analyze each structure step by step.

### Step-by-Step Solution:

1. **Understanding Coordination Number**:
- The coordination number refers to the number of nearest neighbors surrounding a central atom (cation or anion) in a crystal structure.

2. **Analyzing NaCl Structure**:
- In NaCl, Cl⁻ ions form a face-centered cubic (FCC) lattice.
- Na⁺ ions occupy the octahedral voids.
- Each Cl⁻ ion is surrounded by 6 Na⁺ ions, and each Na⁺ ion is also surrounded by 6 Cl⁻ ions.
- **Coordination Number**: Na⁺ = 6, Cl⁻ = 6.
- **Conclusion**: Coordination numbers are the same.

3. **Analyzing CaF₂ Structure**:
- In CaF₂, Ca²⁺ ions form an FCC lattice.
- F⁻ ions occupy all the tetrahedral voids.
- Each Ca²⁺ ion is surrounded by 8 F⁻ ions, while each F⁻ ion is surrounded by only 4 Ca²⁺ ions.
- **Coordination Number**: Ca²⁺ = 8, F⁻ = 4.
- **Conclusion**: Coordination numbers are not the same.

4. **Analyzing Na₂O Structure**:
- In Na₂O, O²⁻ ions form an FCC lattice.
- Na⁺ ions occupy the tetrahedral voids.
- Each O²⁻ ion is surrounded by 4 Na⁺ ions, while each Na⁺ ion is surrounded by 8 O²⁻ ions.
- **Coordination Number**: O²⁻ = 4, Na⁺ = 8.
- **Conclusion**: Coordination numbers are not the same.

5. **Analyzing ZnS (Zinc Blende) Structure**:
- In ZnS, S²⁻ ions form an FCC lattice.
- Zn²⁺ ions occupy alternate tetrahedral voids.
- Each S²⁻ ion is surrounded by 4 Zn²⁺ ions, and each Zn²⁺ ion is also surrounded by 4 S²⁻ ions.
- **Coordination Number**: Zn²⁺ = 4, S²⁻ = 4.
- **Conclusion**: Coordination numbers are the same.

### Final Answer:
The structures where the coordination number for cations and anions is the same are:
- NaCl
- ZnS (Zinc Blende)