Which of the following best describes a closed system?

A closed system is characterized by its ability to exchange energy with its surroundings while not permitting any mass transfer. This means that within the boundaries of the system, energy can enter or leave, often in the form of heat or work, allowing the system to change states or perform tasks. However, the total mass of the closed system remains constant because no material can flow in or out.

This is distinct from an open system, which can exchange both energy and mass, and an isolated system, which does not exchange either with its surroundings. The option relating to the generation of energy does not accurately represent a fundamental aspect of closed systems, since closed systems do not inherently generate energy; they can store, utilize, or transfer it but do not create it from nothing. Therefore, the description of a closed system aligns precisely with the first choice presented.