Which term describes a system where things move in and out of the boundary?

• A. Closed System
• B. Open System
• C. Conductors
• D. Insulators

Answer: (B)

Open systems are those in which the boundary between the system and its surroundings allows matter to cross. In these systems, substances can move in and out, and energy may also cross the boundary depending on the situation. A common example is a pot of boiling water where steam escapes and liquid can be poured out or added, illustrating matter crossing the boundary. This differs from a closed system, where matter does not cross the boundary, even if energy can be exchanged, and from an isolated system, where nothing crosses the boundary at all. Conductors and insulators describe how materials handle electric current, not whether matter crosses a boundary, so they aren’t about the system’s boundary exchange.