What does the second law of thermodynamics state about energy transfer?

The second law of thermodynamics specifically states that heat cannot spontaneously flow from a colder body to a hotter body. This principle establishes the directionality of heat transfer in natural processes and is a key concept in understanding thermodynamic systems.

In practical terms, when two bodies are in thermal contact, heat will flow from the body at a higher temperature to the one at a lower temperature until thermal equilibrium is reached. This law implies that in order for heat to flow from a cooler body to a warmer body, work must be done on the system, such as in refrigeration processes where external energy is used to transfer heat against its natural flow.

The other provided options do not align with the second law's principles. For instance, the creation of energy from nothing is inconsistent with the conservation of energy principle, which holds that energy cannot be created or destroyed. Likewise, the notion of energy transfers being 100% efficient contradicts the second law, which implies that some energy is always lost as waste heat in natural processes. Lastly, the idea that energy can only be lost and never gained is incorrect, as energy can be transferred and transformed in various forms, adhering to the conservation of energy.