A packing of `8:8` co-ordination crystal is present in which of the following compounds?

Options

A. NaCl
B. KCl
C. CsCl
D. `MgF_(2)`

Answer

To determine which compound exhibits an 8:8 coordination packing, we need to analyze the coordination numbers of the ions in each compound. The coordination number indicates how many ions of opposite charge surround a particular ion in the crystal lattice.

### Step-by-Step Solution:

1. **Understanding Coordination Numbers**:
- The coordination number is defined as the number of ions of opposite charge that surround a particular ion in a crystal structure. In this case, we are looking for a compound where one cation coordinates with 8 anions and one anion coordinates with 8 cations, resulting in an 8:8 ratio.

2. **Analyzing the Options**:
- We will evaluate each compound given in the options to find the one with an 8:8 coordination.

3. **Option 1: KCl (Potassium Chloride)**:
- In KCl, the coordination number of K⁺ (potassium) is 6, and the coordination number of Cl⁻ (chloride) is also 6. Thus, the packing is 6:6. This option is incorrect.

4. **Option 2: NaCl (Sodium Chloride)**:
- Similar to KCl, in NaCl, the coordination number of Na⁺ is 6, and the coordination number of Cl⁻ is also 6. Therefore, the packing is 6:6. This option is also incorrect.

5. **Option 3: CsCl (Cesium Chloride)**:
- In CsCl, the coordination number of Cs⁺ is 8, and the coordination number of Cl⁻ is also 8. This gives us an 8:8 packing. This option is correct.

6. **Option 4: MgF₂ (Magnesium Fluoride)**:
- In MgF₂, the coordination number of Mg²⁺ is 6, and the coordination number of F⁻ is 3. This results in a packing of 6:3. This option is incorrect.

7. **Conclusion**:
- The compound that exhibits an 8:8 coordination packing is **CsCl (Cesium Chloride)**.

### Final Answer:
The correct answer is **CsCl (Cesium Chloride)**.