In which of the following structures, the anion has maximum coordination number?

Options

A. NaCl
B. ZnS
C. `CaF_(2)`
D. `Na_(2)O`

Answer

To determine which structure has the anion with the maximum coordination number, we will analyze the coordination numbers of the anions in each of the given structures: NaCl, ZnS, CaF2, and Na2O.

### Step-by-Step Solution:

1. **NaCl Structure:**
- In NaCl, the chloride ion (Cl-) is arranged in a cubic close-packed (CCP) structure.
- Each Cl- ion is surrounded by 6 Na+ ions.
- **Coordination Number of Cl- in NaCl = 6.**

2. **ZnS Structure:**
- ZnS can exist in two forms: Wurtzite and Zinc Blende.
- In the Wurtzite structure, Zn2+ occupies half of the tetrahedral voids, leading to a coordination number of 4 for Zn2+.
- In the Zinc Blende structure, Zn2+ occupies the face-centered cubic (FCC) lattice, while S2- occupies the tetrahedral voids.
- **Coordination Number of S2- in both Wurtzite and Zinc Blende = 4.**

3. **CaF2 Structure:**
- In CaF2, calcium ions (Ca2+) occupy the cubic close-packed (CCP) lattice.
- The fluoride ions (F-) occupy the tetrahedral voids.
- Each Ca2+ ion is surrounded by 8 F- ions.
- **Coordination Number of F- in CaF2 = 8.**

4. **Na2O Structure:**
- In Na2O, the oxide ion (O2-) is in a cubic close-packed (CCP) structure.
- Each O2- ion is surrounded by 8 Na+ ions in tetrahedral voids.
- **Coordination Number of O2- in Na2O = 4.**

### Conclusion:
Comparing the coordination numbers:
- NaCl: Cl- has a coordination number of 6.
- ZnS: S2- has a coordination number of 4.
- CaF2: F- has a coordination number of 8.
- Na2O: O2- has a coordination number of 4.

The maximum coordination number among these is found in **CaF2**, where the fluoride ion (F-) has a coordination number of 8.

### Final Answer:
The structure in which the anion has the maximum coordination number is **CaF2**.

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