Final answer:
A gas spreads out to fill any container, as it has neither a definite shape nor a definite volume.
Step-by-step explanation:
The state of matter that spreads out to fill any container that holds it is a gas. Unlike solids which have a definite shape and volume, and liquids which have a definite volume but take the shape of their container, gases have neither a definite shape nor a definite volume. When a gas is placed in a container, its molecules move rapidly in all directions, filling the entire space available to them. This characteristic of gas is due to the weak forces of attraction between its molecules, allowing them to move freely and occupy the entire volume of their container.