* Pure Substance: A pure substance is made up of only one type of particle.

* Chemical Element: A chemical element is a substance that cannot be broken down into simpler substances by chemical means. It's the simplest form of matter.

Hydrogen (H) and chlorine (Cl) fit both definitions. They are both pure substances because they consist of only hydrogen atoms and chlorine atoms, respectively. They are also chemical elements because they can't be broken down into simpler substances.

Therefore, hydrogen and chlorine are both pure substances and chemical elements.