Which is incorrect statement?

Options

A. In NaCl structure, tetrahedral voids are unoccupied
B. In ZnS structure, octahedral voids are unoccupied
C. In `CaF_(2)` structure, all tetrahedral voids are occupied
D. In `Na_(2)O` structure, all tetrahedral voids are unoccupied

Answer

To determine which statement is incorrect regarding the structures of ionic compounds, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding NaCl Structure:**
- NaCl has a face-centered cubic (FCC) structure.
- In this structure, chloride ions (Cl⁻) occupy the FCC lattice positions.
- Sodium ions (Na⁺) occupy the octahedral voids.
- **Statement:** "In NaCl structure, tetrahedral voids are unoccupied."
- **Analysis:** This statement is true because all octahedral voids are occupied by Na⁺ ions, leaving the tetrahedral voids unoccupied.

2. **Understanding Zinc Sulfide Structure:**
- Zinc sulfide (ZnS) also has an FCC structure.
- In this case, sulfide ions (S²⁻) occupy the FCC lattice positions.
- Zinc ions (Zn²⁺) occupy half of the tetrahedral voids.
- **Statement:** "In zinc sulfide structure, octahedral voids are unoccupied."
- **Analysis:** This statement is true because if the tetrahedral voids are occupied by Zn²⁺ ions, the octahedral voids remain unoccupied.

3. **Understanding Calcium Fluoride Structure:**
- Calcium fluoride (CaF₂) has an FCC structure.
- Calcium ions (Ca²⁺) occupy the FCC lattice positions.
- Fluoride ions (F⁻) occupy all the tetrahedral voids.
- **Statement:** "In calcium fluoride CaF2, all tetrahedral voids are occupied."
- **Analysis:** This statement is true as all tetrahedral voids are indeed occupied by fluoride ions.

4. **Understanding Sodium Oxide Structure:**
- Sodium oxide (Na₂O) has an FCC structure.
- Oxide ions (O²⁻) occupy the lattice positions.
- Sodium ions (Na⁺) occupy all the tetrahedral voids.
- **Statement:** "In Na2O structure, all tetrahedral voids are unoccupied."
- **Analysis:** This statement is incorrect because all tetrahedral voids are actually occupied by Na⁺ ions.

### Conclusion:
The incorrect statement among the given options is: **"In Na2O structure, all tetrahedral voids are unoccupied."**

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