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. **Understanding the Triple Point**:
The triple point of a substance is the specific temperature and pressure at which the three phases (solid, liquid, and vapor) coexist in thermodynamic equilibrium. For water, this occurs at 0.01°C and a pressure of 611.657 pascals.

**Hint**: Remember that at the triple point, all three phases are in equilibrium.

2. **Equilibrium of Phases**:
At the triple point, the solid, liquid, and vapor phases of water exist simultaneously. This means that the physical properties, including temperature and pressure, are the same for all three phases.

**Hint**: Consider how equilibrium affects the properties of the phases.

3. **Average Kinetic Energy**:
The average kinetic energy of molecules in any phase is directly related to the temperature of that phase. Since all three phases (solid, liquid, vapor) are at the same temperature at the triple point, the average kinetic energy of the molecules in each phase will also be the same.

**Hint**: Recall the relationship between temperature and kinetic energy.

4. **Conclusion**:
Therefore, at the triple point, the average kinetic energy of the water molecules in the solid, liquid, and vapor states is equal.

**Final Answer**: The average kinetic energy of the water molecule at the triple point is the same for all three states.

### Summary:
At the triple point, since all three phases coexist in equilibrium and are at the same temperature, the average kinetic energy of the water molecules is identical across solid, liquid, and vapor states.