The average kinetic energy of water molecules increases when -

A: H2O (s) changes to H2O (l) at 0°C

B: H2O (l) changes to H2O (s) at 0°C

C: H2O (l) at 10°C changes to H2O (l) at 20°C

D: H2O (l) at 20°C changes to H2O (l) at 10°C

Answer: option C: H2O (l) at 10°C changes to H2O (l) at 20°C

Explanation:

To solve this questions use the fact the temperature is a measure of the average kinetic energy of the particles of a substance.

For a given substance, the higher the temperature the higher kinetic energy, the lower the temperature the lower the kinetic energy

That is a statement derived from the kinetic theory.

The kinetic energy states that as the temperature of a substance increases, so do the average velocity of its particles and so the average kinetic energy.

Thas is why gases have a higher kinetic energy than liquids and liquids have a higher kinetic energy than solids.

The options A : H2O (s) changes to H2O (l) at 0°C and B: H2O (l) changes to H2O (s) at 0°C describe changes at constant temperature, so in them the average kinetic energy does not change.

The option C: H2O (l) at 10°C changes to H2O (l) at 20°C, as said, is the right answer because it is a process in which the temperature is increasing, so the average kinetiic energy is also increasing.

The option D: H2O (l) at 20°C changes to H2O (l) at 10°C corresponds to a decrease of the kinetic energy, since the temperature is decreasing.