Which of the following terms describes a substance that cannot be broken down into a simpler substance?

An element is defined as a pure substance that cannot be broken down into simpler substances through chemical means. Elements are the basic building blocks of matter and are made up of atoms, which are the smallest units of chemical elements. There are currently 118 known elements, each with unique properties.

Molecules, on the other hand, are formed when two or more atoms bond together, and compounds are a type of molecule that consists of at least two different elements. Therefore, while molecules and compounds can be decomposed into their constituent elements, an element itself remains indivisible in terms of simpler chemical substances. This is why the term that best describes a substance that cannot be further broken down is an element.