A closed flask contains water in all its three states solid, liquid and vapour at `0^(@)C`. In this situation, the average kinetic energy of water molecules will be

Options

A. the greatest in all the three states
B. the greatest in vapour state
C. the greatest in the liquid state
D. the greatest in the solid state

Explanation

To determine the average kinetic energy of water molecules in a closed flask containing water in all three states (solid, liquid, and vapor) at 0°C, we will analyze the kinetic energy associated with each state of matter.

### Step-by-Step Solution:

1. **Understanding States of Matter**:
- Water exists in three states: solid (ice), liquid (water), and vapor (steam).
- At 0°C, all three states can coexist in equilibrium.

2. **Kinetic Energy in Solids**:
- In the solid state (ice), water molecules are closely packed and can only vibrate around fixed positions.
- The average kinetic energy of molecules in the solid state is low due to limited movement.
- **Kinetic Energy (KE) in solid**: Negligible.

3. **Kinetic Energy in Liquids**:
- In the liquid state, water molecules are more loosely packed compared to solids and can move past each other.
- The average kinetic energy of molecules in the liquid state is higher than in the solid state due to increased molecular motion.
- **Kinetic Energy (KE) in liquid**: Moderate.

4. **Kinetic Energy in Gases**:
- In the vapor state, water molecules are far apart and move freely at high speeds.
- The average kinetic energy of molecules in the vapor state is the highest among the three states due to the high velocity of the molecules.
- **Kinetic Energy (KE) in vapor**: Maximum.

5. **Comparison of Kinetic Energies**:
- The average kinetic energy of water molecules in the three states at 0°C can be summarized as:
- Solid (ice): Negligible
- Liquid (water): Moderate
- Vapor (steam): Maximum
- Therefore, the average kinetic energy of water molecules is greatest in the vapor state.

### Conclusion:
The average kinetic energy of water molecules in a closed flask containing water in all three states at 0°C is maximum in the vapor state.