In a NaCl structure, if positions of Na atoms and Cl - atoms are interchanged, then in the new unit cell

Options

A. Na atoms is present at body centre
B. Cl atom is present at face centre
C. Na atom is present in tetrahedral voids
D. Cl atoms is present in octahedral voids

Answer

To solve the question regarding the interchange of positions of Na and Cl atoms in a NaCl structure, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the NaCl Structure**:
- In a normal NaCl structure, sodium ions (Na⁺) are located at the octahedral voids, while chloride ions (Cl⁻) are arranged in a face-centered cubic (FCC) lattice.

2. **Interchanging Positions**:
- When we interchange the positions of Na and Cl, the sodium ions will now occupy the positions that were previously occupied by the chloride ions (the FCC lattice), and the chloride ions will occupy the octahedral voids.

3. **Identifying the New Positions**:
- After the interchange:
- Na⁺ ions will be at the FCC lattice points (which are the face centers of the cube).
- Cl⁻ ions will occupy the octahedral voids.

4. **Analyzing the Options**:
- **Option 1**: Sodium atom is present at body center - **Incorrect**. There are no atoms at the body center in either structure.
- **Option 2**: Chlorine atom is present at face center - **Incorrect**. Chlorine occupies octahedral voids, not face centers.
- **Option 3**: Sodium atom is present at tetrahedral voids - **Incorrect**. Sodium occupies the FCC arrangement, not tetrahedral voids.
- **Option 4**: Chlorine atom is present in the octahedral voids - **Correct**. This is consistent with our analysis.

5. **Conclusion**:
- The correct answer is that chlorine atoms are present in the octahedral voids after the interchange of positions.

### Final Answer:
The correct option is **4**: Chlorine atom is present in the octahedral voids.