Which of the following best describes thermal energy?

The best description of thermal energy is that it refers to the total energy associated with the motion of particles. This concept is rooted in the understanding that thermal energy is a form of kinetic energy; as particles within a substance move more rapidly, the temperature of that substance increases, indicating higher thermal energy. In essence, thermal energy is indicative of the internal energy present in a system due to the random motion of its microscopic constituents, such as atoms and molecules.

The other options do not capture the essence of thermal energy. The ability to cause chemical reactions relates to chemical energy, the energy in a flowing electric circuit pertains to electrical energy, and energy produced from fossil fuels typically refers to chemical energy that is transformed into thermal or mechanical energy when combusted. None of these accurately reflect the characteristics of thermal energy, which is fundamentally tied to the motion and arrangement of particles.