Final answer:
In an isolated system, such as a closed container, the mass remains constant and cannot enter or exit the system.
Step-by-step explanation:
In an isolated system, such as a closed container, the mass remains constant. In other words, mass cannot enter or exit an isolated system. It is a fundamental principle of physics known as the conservation of mass.
For example, if you have a sealed box with a fixed amount of air inside, no additional air particles can enter or leave the box. The total mass of the air inside the box will always remain the same.