Final answer:
The state of matter where molecules move apart to fill its container is called gaseous state. In this state, molecules are energetic and move freely, in contrast to solid or liquid states where molecules are closer.
Step-by-step explanation:
When molecules move apart, causing the substance to fill its container, the substance is in a gaseous state. In the gaseous state, molecules have a lot of energy and move freely around, which allows them to fill the container they're in. This is different from a solid or a liquid state where the molecules are much closer together.For example, when water boils and turns into steam, the water molecules move apart and fill the container, resulting in a gaseous state of matter.
Learn more about States of Matter