The form of a compound that changes both its shape and volume is called a gas.

Here's why:

* Gases have no fixed shape or volume. They will take the shape of their container and expand to fill the entire space available. This is because the particles in a gas are far apart and move freely.

* Liquids have a fixed volume but not a fixed shape. They will take the shape of their container but will not necessarily fill the entire space.

* Solids have a fixed shape and volume. They maintain their shape and volume regardless of the container they are in.