8:8 coordination of CsCl is found to change into 6:6 coordination :

Options

A. Applying pressure
B. Increasing temperature
C. Both A and B
D. None of these

Answer

To solve the question regarding the change in coordination of CsCl from 8:8 to 6:6, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Coordination Numbers**:
- Coordination number refers to the number of nearest neighbors surrounding an atom in a crystal lattice. In this case, CsCl has a coordination number of 8:8, meaning each Cs+ ion is surrounded by 8 Cl- ions and vice versa.

2. **Effect of Temperature**:
- As the temperature of a system increases, the kinetic energy of the particles also increases. This increased energy causes the particles to move more vigorously.

3. **Change in Crystal Structure**:
- With the increase in temperature, the crystal structure of CsCl can change. The higher energy allows the ions to overcome some of the attractive forces holding them in the 8:8 coordination.

4. **Transition from 8:8 to 6:6 Coordination**:
- At elevated temperatures, the CsCl structure can transition from an 8:8 coordination to a 6:6 coordination. This means that each Cs+ ion is now surrounded by only 6 Cl- ions and vice versa.

5. **Effect of Pressure**:
- Conversely, applying high pressure to the system tends to stabilize the higher coordination number (8:8). Therefore, high pressure would push the system back to the 8:8 coordination from 6:6.

6. **Conclusion**:
- The only condition that causes the transition from 8:8 coordination to 6:6 coordination in CsCl is an increase in temperature.

### Final Answer:
The change from 8:8 coordination of CsCl to 6:6 coordination occurs with an **increase in temperature**.