The point at which densities of a substance in gaseous as well as in liquid state are same called

Options

A. Critical point
B. Isoelectric point
C. Isotonic point
D. Ideal point

Answer

To solve the question, we need to identify the term that describes the point at which the densities of a substance in both its gaseous and liquid states are the same.

### Step-by-Step Solution:

1. **Understanding the Concept**:
- The question refers to a specific condition in the phase diagram of a substance where the densities of the liquid and gas phases become equal. This condition is crucial in understanding phase transitions.

2. **Identifying the Term**:
- The point at which the densities of a substance in its liquid and gaseous states are equal is known as the "critical point." At this point, the distinction between the liquid and gas phases disappears, and they can coexist in a state known as a supercritical fluid.

3. **Critical Temperature and Pressure**:
- The critical point is defined by two parameters: critical temperature and critical pressure. Above the critical temperature, a substance cannot exist in the liquid state, regardless of the pressure applied.

4. **Conclusion**:
- Therefore, the answer to the question is that the point at which the densities of a substance in gaseous and liquid states are the same is called the "critical point."

### Final Answer:
The point at which the densities of a substance in gaseous as well as in liquid state are the same is called the **critical point**.