Answer:
Gas.
Step-by-step explanation:
Matter can be found in nature in three states: solid, liquid, and gas. The main difference between these three states is the separation of its molecules.
A solid has a definite form, its molecules are closely packed together and there is little to no movement between each molecule. When put in a container, it retains its form.
A liquid does not have a definite form, its molecules can move past another and they are not as close as in a solid, but it is not as loose either. When put in a container, it takes the shape of the container but it has a defined surface.
A gas does not have a definite form, its molecules are totally free from one another and the distance that separates them is much larger than the size they have. When placed in a container, they spread out completely and fill the entire shape of the container.