CsCl structure is interchanged into NaCl structure. This can be done because

Options

A. (A) Temperature is increased
B. (B) pressure is decreased
C. (C) Temperature is decreased
D. (D) pressure is increased

Answer

To determine the conditions under which the CsCl structure can be interchanged into the NaCl structure, we need to analyze the characteristics of both structures and the factors affecting coordination numbers.

### Step-by-Step Solution:

1. **Understanding CsCl Structure**:
- The CsCl (Cesium Chloride) structure is a body-centered cubic (BCC) lattice.
- In this structure, both Cs⁺ and Cl⁻ ions have a coordination number of 8. This means each Cs⁺ ion is surrounded by 8 Cl⁻ ions and vice versa.

2. **Understanding NaCl Structure**:
- The NaCl (Sodium Chloride) structure is a face-centered cubic (FCC) lattice.
- In the NaCl structure, the coordination number is 6 for both Na⁺ and Cl⁻ ions. Each Na⁺ ion is surrounded by 6 Cl⁻ ions and vice versa.

3. **Comparing Coordination Numbers**:
- The transition from CsCl to NaCl involves a change in coordination number from 8:8 to 6:6. This indicates a decrease in the coordination number.

4. **Factors Affecting Coordination Number**:
- The coordination number can decrease due to two main factors:
- **Increase in Temperature**: When temperature increases, the kinetic energy of ions increases, causing them to move further apart. This can lead to a decrease in the coordination number.
- **Decrease in Pressure**: Lowering the pressure allows the ions to spread out, which can also result in a decrease in coordination number.

5. **Conclusion**:
- Therefore, the conversion of the CsCl structure to the NaCl structure can occur when the temperature is increased and/or when the pressure is decreased.

### Final Answer:
The CsCl structure can be interchanged into the NaCl structure because:
- **A**: Temperature is increased.
- **B**: Pressure is decreased.