In `Na_2 O` structure

Options

A. `O^(2-)` ions constitute CCP and `Na^+` ions occupy all the octahedral holes
B. `O^(2-)` ions constitute CCP and `Na^+` ions occupy all the tetrahedral holes
C. `O^(2-)` ions constitute CCP and `Na^+` ions occupy 50% of tetrahedral holes and 100% octahedral holes
D. `Na^+` ions constitute CCP and `O^(2-)` ions occupy half of octahedral holes

Answer

To solve the question regarding the structure of Na2O, we will analyze the arrangement of ions in the crystal lattice and determine which of the given options accurately describes this structure.

### Step-by-Step Solution:

1. **Identify the Ions in Na2O**:
- Sodium oxide (Na2O) consists of sodium ions (Na⁺) and oxide ions (O²⁻).
- There are two sodium ions for every oxide ion in the formula.

2. **Understand the Size of Ions**:
- Sodium ions (Na⁺) are smaller in size compared to oxide ions (O²⁻). This is significant because smaller ions typically occupy the voids in a crystal lattice formed by larger ions.

3. **Determine the Arrangement of Oxide Ions**:
- The oxide ions (O²⁻) are arranged in a close-packed structure. In this case, they form a cubic close-packed (CCP) or face-centered cubic (FCC) arrangement.
- In this arrangement, the oxide ions occupy the corners and the face centers of the cubic unit cell.

4. **Calculate the Number of Ions in the Unit Cell**:
- In a CCP structure, there are 4 oxide ions per unit cell (8 corners × 1/8 contribution + 6 faces × 1/2 contribution = 4).

5. **Identify the Tetrahedral and Octahedral Voids**:
- In a CCP structure, there are 8 tetrahedral voids and 4 octahedral voids per unit cell.
- Since Na⁺ ions are smaller, they will occupy the tetrahedral voids.

6. **Determine the Occupation of Voids**:
- Given that there are 8 tetrahedral voids and 2 Na⁺ ions, all of the tetrahedral voids will be occupied by Na⁺ ions.

7. **Evaluate the Options**:
- **Option 1**: O²⁻ ions constitute CCP and Na⁺ occupies octahedral holes. (Incorrect)
- **Option 2**: O²⁻ ions constitute CCP and Na⁺ occupies all tetrahedral holes. (Correct)
- **Option 3**: O²⁻ constitutes CCP, Na⁺ occupies 50% of tetrahedral and 100% octahedral holes. (Incorrect)
- **Option 4**: Na⁺ constitutes CCP and O²⁻ occupies half of the octahedral holes. (Incorrect)

8. **Conclusion**:
- The correct option that describes the Na2O structure is **Option 2**: O²⁻ ions constitute CCP and Na⁺ occupies all tetrahedral holes.