When density of liquid and vapours becomes the same the clear boundary between liquid and vapours disappear the temperature is called

Options

A. Boyle's temperature
B. melting point
C. critical temperature
D. none of the above

Answer

To solve the question, we need to identify the temperature at which the density of a liquid and its vapor becomes the same, resulting in the disappearance of the clear boundary between the two phases.

### Step-by-Step Solution:

1. **Understanding the Phases**:
- In a typical scenario, a liquid (e.g., water) exists alongside its vapor in a closed container. At normal conditions, there is a distinct boundary between the liquid and vapor phases.

**Hint**: Think about how liquids and gases behave under different temperatures and pressures.

2. **Effect of Temperature**:
- As we increase the temperature of the liquid, the kinetic energy of the molecules increases. This can lead to changes in the state of matter from liquid to vapor.

**Hint**: Consider what happens to the molecules in a liquid as they gain energy.

3. **Critical Point Concept**:
- There comes a point where the temperature is high enough that the density of the liquid and vapor becomes equal. At this point, the two phases can no longer be distinguished from one another.

**Hint**: Recall the definition of the critical point in thermodynamics.

4. **Identifying the Temperature**:
- The temperature at which this phenomenon occurs is known as the **critical temperature**. At this temperature, the liquid and vapor phases merge into a single phase called a supercritical fluid.

**Hint**: Remember that the critical temperature is a specific term used in phase diagrams.

5. **Conclusion**:
- Therefore, the correct answer to the question is **critical point**.

### Final Answer:
The temperature at which the density of liquid and vapor becomes the same, causing the clear boundary between them to disappear, is called the **critical point**.