why do different substances have different melting points? hydrogen bonds different sizes of electrons…

Brief Explanations:

The melting - point of a substance depends on the strength of the forces between its molecules. Different substances have different levels of intermolecular attraction. Hydrogen bonds are just one type of intermolecular force. The fact that molecules move faster when heated is related to the general concept of heating but not the reason for different melting points among substances. Electrons do not have different sizes in the context of explaining melting points. The key factor is the varying levels of attraction between molecules.

Answer:

D. Different levels of attraction between molecules