Which of the following statement is correct ?

Options

A. On increasing temperature the coordination number of solid remains unchanged
B. On increasing pressure the coordination number of solid increases
C. On increasing temperature the coordination number of solid increases
D. On increasing pressure the coordination number of solid decreases

Answer

To determine which statement is correct regarding the relationship between coordination number (CO2), temperature, and pressure, we can analyze the effects of pressure and temperature on the coordination number of solids.

### Step-by-Step Solution:

1. **Understanding Coordination Number (CO2)**:
- The coordination number refers to the number of nearest neighbors surrounding a central atom in a solid structure.

2. **Effect of Pressure on Coordination Number**:
- When pressure increases, atoms are forced closer together. This can lead to an increase in the coordination number.
- For example, if the initial coordination number is 6, applying pressure can increase it to 8 or even 10.

3. **Effect of Temperature on Coordination Number**:
- When temperature increases, atoms gain kinetic energy and tend to move further apart. This results in a decrease in the coordination number.
- Therefore, if the temperature rises, the coordination number is likely to decrease.

4. **Analyzing the Statements**:
- **Statement 1**: "On increasing the temperature, the CO2 remains unchanged."
- This is incorrect because an increase in temperature typically decreases the coordination number.
- **Statement 2**: "On increasing the pressure, the CO2 increases."
- This is correct as increased pressure leads to a higher coordination number.
- **Statement 3**: "On increasing the temperature, CO2 increases."
- This is incorrect since an increase in temperature leads to a decrease in coordination number.
- **Statement 4**: "Coordination number of solid is not increasing."
- This is incorrect because the coordination number can increase with pressure.
- **Statement 5**: "On increasing the pressure, Coordination number of solid decreases."
- This is incorrect as increased pressure leads to an increase in coordination number.

5. **Conclusion**:
- The only correct statement is: "On increasing the pressure, the CO2 increases."

### Final Answer:
The correct statement is: **"On increasing the pressure, the CO2 increases."**