Here's why:

* Elements are pure substances that cannot be broken down into simpler substances by chemical means. They are the building blocks of all matter.

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

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

Cadmium is a single, pure substance found on the periodic table. It cannot be broken down into simpler substances.