In a closed system, what can be said about the matter?

In a closed system, the defining characteristic is that matter cannot enter or leave the system. This means that any processes occurring within the system must involve only the matter that is already contained inside. The total amount of matter remains constant over time, as there is no exchange of matter with the surroundings.

This principle is fundamental in various scientific disciplines, including thermodynamics, where it helps to analyze energy and material exchanges without the influence of external factors. While the matter within the system can change in form or state through chemical reactions or physical changes, the total quantity of matter remains unchanged, which is why this option accurately describes the nature of matter in a closed system.