Here's why:

* Elements are the simplest pure substances that cannot be broken down into simpler substances by ordinary chemical means. Iron is found on the periodic table, which lists all the known elements.

* Compounds are formed when two or more elements chemically combine in a fixed ratio. For example, iron oxide (rust) is a compound made of iron and oxygen.

* Mixtures are combinations of two or more substances that are not chemically bonded. They can be separated by physical means. For example, sand and iron filings would make a mixture.