Here's why:

* Elements are the simplest pure substances. They cannot be broken down into simpler substances by chemical means.

* Mixtures are combinations of two or more substances that are not chemically bonded. The substances in a mixture can be separated by physical means.

* Compounds are formed when two or more elements chemically combine in a fixed ratio.

Iron is a pure substance that cannot be broken down further. It appears on the periodic table as a single element, meaning it is not made up of other elements.