A substance that cannot be broken down into simpler substances is called an element.

Elements are the fundamental building blocks of all matter. They are made up of only one type of atom. Examples of elements include:

* Hydrogen (H)

* Oxygen (O)

* Carbon (C)

* Gold (Au)

* Iron (Fe)

While elements cannot be broken down into simpler substances by ordinary chemical means, they can be broken down into subatomic particles (protons, neutrons, and electrons) through nuclear reactions.