Final answer:
The water molecules with the highest average kinetic energy are in sample A which is at 100°C. Volume does not affect kinetic energy, only temperature does, and since sample A has the highest temperature, it also has the highest kinetic energy of the molecules.
Step-by-step explanation:
The question is related to the kinetic energy of water molecules at different temperatures and volumes. According to the kinetic theory of matter, the average kinetic energy of the molecules of a substance is directly proportional to the temperature of the substance (measured in Kelvin). This implies that the higher the temperature, the higher the kinetic energy of the molecules. Therefore, the volume of water doesn't affect the average kinetic energy, but the temperature does.
To find out in which sample of water the molecules have the highest average kinetic energy, you compare the temperatures provided, remembering that temperature needs to be in Kelvin for direct comparison related to kinetic energy. However, since the question provides temperatures in degrees Celsius, and our comparison is relative, we can use the temperatures as they are because the temperature difference is the same whether in Celsius or Kelvin.
Among the options given (A) 20. mL at 100°C, (B) 40. mL at 80.°C, (C) 60. mL at 60°C, and (D) 80. mL at 40.°C, sample A at 100°C has the highest temperature. This means that the water molecules in sample A have the highest average kinetic energy.