The method of heat transfer involving the flow of heat from molecule to molecule is called:

Conduction is the method of heat transfer that occurs through the direct contact of molecules. When one molecule is heated, it gains energy and vibrates more rapidly. This energy is then passed to neighboring molecules through collisions, allowing heat to transfer through the material without any movement of the substance itself. This process is particularly effective in solids, where the closely packed molecules can easily transfer energy between each other.

In contrast, convection involves the transfer of heat through the movement of fluids (liquids or gases), where warmer areas of the fluid rise, and cooler areas sink, creating currents. Radiation refers to the transfer of heat through electromagnetic waves and does not require a medium (it can occur in a vacuum). Expansion is more related to the change in volume of a substance as it is heated rather than a method of heat transfer. Thus, conduction accurately describes the molecular-level transfer of heat energy, making it the correct choice in this scenario.