Correct Answer: Open system

Solution : The correct option is open system.

Warming ammonium chloride with sodium hydroxide in a test tube is a common example of an open system. In an open system, both matter and energy may be exchanged with the environment. When ammonium chloride is burned with sodium hydroxide, it produces ammonia gas (NH3) and water vapour (H2O). Both the gas and the vapour can escape into the surrounding environment, and this interchange of materials with the surroundings defines an open system.