Identify the correct statement(s)

Options

A. CsCl changes to NaCl structure on heating
B. NaCl changes to CsCl structure on applying pressure
C. Coordination number increases on applying pressure
D. Coordination number increase on heating.

Explanation

To solve the question "Identify the correct statement(s)", we will analyze each statement provided in the options step by step.

### Step-by-Step Solution:

1. **Statement 1: CSCl changes to NaCl structure on heating.**
- **Analysis**: This statement suggests that when CsCl (cesium chloride) is heated, it transforms into the NaCl (sodium chloride) structure. However, this transformation is not feasible because the crystal structures of CsCl and NaCl are fundamentally different. CsCl has a simple cubic structure, while NaCl has a face-centered cubic structure. Heating does not change the fundamental arrangement of ions in a crystal lattice.
- **Conclusion**: This statement is **incorrect**.

2. **Statement 2: NaCl changes to CsCl structure on applying pressure.**
- **Analysis**: This statement implies that applying pressure to NaCl will cause it to adopt the CsCl structure. Similar to the first statement, this is not possible. The structural arrangements of NaCl and CsCl are distinct, and applying pressure does not lead to a transformation from one structure to another.
- **Conclusion**: This statement is **incorrect**.

3. **Statement 3: Coordination number increases on applying pressure.**
- **Analysis**: This statement is valid. When pressure is applied to a crystal lattice, the atoms or ions are forced closer together. As they come closer, the number of nearest neighbors (coordination number) increases. For example, in a body-centered cubic structure, the coordination number is 8, while in a face-centered cubic structure, it is 12. When pressure is applied, the atoms can occupy positions that increase the coordination number.
- **Conclusion**: This statement is **correct**.

### Final Conclusion:
The only correct statement among the options is **Statement 3**: Coordination number increases on applying pressure.