Which describes a closed system's interaction with external matter?

In thermodynamics, a closed system is defined explicitly by its ability to exchange energy but not matter with its surroundings. This means that while energy can enter or exit the system (for example, in the form of heat or work), the total amount of matter within the closed system remains constant over time.

Choosing the description that states a closed system does not allow matter to enter or leave accurately captures this principle. It highlights the primary characteristic of closed systems, differentiating them from open systems, where both energy and matter can flow in and out, and isolated systems, where neither can transfer with the surroundings.

Understanding this distinction is crucial for studying thermodynamic processes, as it helps in predicting how a system will react to changes when subjected to various energy exchanges without altering its mass. This concept is foundational for analyzing many practical scenarios in thermodynamic systems.