The kinetic energy of water molecules is directly related to the temperature of the water. The higher the temperature, the more kinetic energy the molecules have.
From the given temperatures:
- Sample 1: 98.2 °C
- Sample 2: 46.0 °C
- Sample 3: 100.6 °C
- Sample 4: 31.4 °C
Sample 4 has the lowest temperature at 31.4 °C. Therefore, it has the lowest kinetic energy.
The correct answer is 4.