Which term describes a system in which nothing can escape?

• A. Closed System
• B. Open System
• C. Efficiency
• D. Perpetual Motion Machines

Answer: (A)

Think about how a system interacts with what’s around it. If nothing inside can get out, you’re describing a closed system—the materials stay inside the boundaries. In many classroom contexts, matter can’t cross the boundary in a closed system, while energy might still be exchanged. An open system would let matter cross the boundary, which would mean stuff could escape. The other choices aren’t about containing matter: efficiency is a ratio that measures how well a process uses energy, and perpetual motion machines describe a hypothetical device that would violate basic physical laws, not a way a system is bounded.