Here's why:

* Solid Iron: Solid iron is a rigid material and will not take the shape of its container. It has a definite shape and volume. Think of a metal bar or a piece of iron cookware.

* Liquid Iron: Liquid iron, like any liquid, will take the shape of its container. It flows and conforms to the container's shape. However, liquid iron is extremely hot and dangerous to handle.

* Gaseous Iron: Gaseous iron is not a common state we encounter, as iron boils at a very high temperature. But if you could create gaseous iron, it would also fill the entire volume of its container, just like any gas.

Let me know if you'd like to know more about the states of matter!