A closed flask contains a substance in all its three states, solids, liquids and vapour at its triple point. In this situation the average KE of the water molecule will be

Options

A. Maximum in vapour state
B. Maximum in solid state
C. Greater in the liquid than in vapour state
D. Same in all the three states

Answer

To solve the question regarding the average kinetic energy (KE) of water molecules at the triple point, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Triple Point**:
- The triple point of a substance is the specific temperature and pressure at which all three phases (solid, liquid, and gas) coexist in thermodynamic equilibrium.

2. **Identify the Relationship Between Kinetic Energy and Temperature**:
- The average kinetic energy of molecules in a substance is directly proportional to its temperature. This means that regardless of the state (solid, liquid, or gas), the average kinetic energy is determined by the temperature of the system.

3. **Recognize the Independence from State**:
- The average kinetic energy of water molecules does not depend on whether the water is in solid, liquid, or vapor form. It only depends on the temperature at which the system is maintained.

4. **Conclusion**:
- Since at the triple point, all three states of water (solid, liquid, and vapor) are in equilibrium at the same temperature, the average kinetic energy of the water molecules will be the same across all three states.

5. **Final Answer**:
- Therefore, the average kinetic energy of the water molecules at the triple point is the same in all three states.