1)

An experimenter notices that the state of matter of a pure substance changes from a liquid to a gas. Which question is most relevant to ask regarding this change?

A) How much energy is required for condensation?

B) What caused a change in the charge of the particles in the substance?

C) How much energy was added to the substance to increase molecule motion?

D) How did a decrease in kinetic energy of the molecules result in a phase change?

C) How much energy was added to the substance to increase molecule motion?

Explanation:

The most relevant question to ask regarding this change must take into account the physical knowledge about matter.

When matter changes from liquid state to gaseous state, a physical change called evaporation, the particles (molecules or atoms) of the pure substance will separate from each other, take up more space and move faster.

Condensation is the opposite to evaporation, thus the option A) is not the most relevant question.

The charge of the particles does not change; so the option B) is not relevant at all.

The particles should gain energy from the surroundings to increase their motion (kinetic energy) when they pass from liquid state, where they move slower, to gas state, where they move faster. Hence, the option C), How much energy was added to the substance to increase molecule motion?, is totally relevant.

Since this is an increase in the kinetic energy of the molecules, the option D) is not relevant.