The principle stating that matter cannot be created or destroyed, but can change form is known as what?

The principle that matter cannot be created or destroyed, but can change form, is best described by the law of conservation of mass. This law indicates that the mass of a closed system will remain constant over time, regardless of the processes happening within that system. This foundational concept in physics and chemistry emphasizes that when matter undergoes a chemical reaction, for instance, the total amount of matter remains unchanged even though it may transform into different substances.

The law of conservation of energy, while related, specifically pertains to energy rather than matter. It states that the total energy in a closed system remains constant, although it can change forms, such as from kinetic energy to potential energy. The law of thermodynamics, which involves various energy transformations and the flow of heat, does not directly address the conservation of mass.

Overall, while options may touch on related themes, the law of conservation of mass is the most accurate descriptor of the principle that outlines the invariant nature of matter in terms of its existence and transformation.