If a substance is at its melting or boiling point, as the heat content of the sample of matter increases, its temperature increases the number of intermolecular bonds decreases the space between particles increases the particles move faster

the space between particles

increases the particles move faster

Explanation:

Melting and boiling points are phase changes as a result of heating of substances.

When a substance is heated, the heat content of its matter increases. In this regard, temperature rises and reaches a point where it steadies. A phase change occurs here. Most times, heat gives more energy to particles that makes up a substance. This makes intermolecular vibrations to increase and as it reaches the boiling and melting point, molecules can break free and be independent. Sometimes they flow freely.

This simply implies that there is more intermolecular space for them to move and the particles are able to move more freely.

i'm assuming that the correct answer is indeed the first one/ "a"..