Coordination number of NaCl crystal will be :

Options

A. `8:8`
B. `6:6`
C. `4:4`
D. `2:2`

Answer

To determine the coordination number of NaCl crystal, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure of NaCl**:
- NaCl crystallizes in a face-centered cubic (FCC) lattice structure where Cl⁻ ions are arranged in the FCC lattice.

2. **Determine the Position of Ions**:
- In the FCC lattice, there are 4 Cl⁻ ions per unit cell. The Na⁺ ions occupy the octahedral voids in this structure.

3. **Count the Octahedral Voids**:
- In an FCC structure, there are 4 octahedral voids per unit cell. Each Na⁺ ion occupies one of these voids.

4. **Understanding Coordination Number**:
- The coordination number of an ion in a crystal structure is defined as the number of nearest neighboring ions surrounding it.

5. **Calculate the Coordination Number**:
- For Na⁺ ions in the octahedral voids, the coordination number is 6. This means each Na⁺ ion is surrounded by 6 Cl⁻ ions.
- Since the Na⁺ and Cl⁻ ions are in a 1:1 ratio, the coordination number for Cl⁻ ions is also 6.

6. **Conclusion**:
- Therefore, the coordination number of NaCl crystal is 6.

### Final Answer:
The coordination number of NaCl crystal is 6.

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