Which of the following best describes an element?

An element is defined as a pure substance that cannot be broken down into simpler substances by chemical means. This fundamental characteristic distinguishes elements from compounds and mixtures. Each element is made up of only one kind of atom and retains unique properties that are not found in simpler forms.

For example, elements like hydrogen, oxygen, and gold are pure substances that consist of only one type of atom and cannot be decomposed into any simpler chemical entities. In contrast, compounds consist of two or more elements that are chemically bonded, and these compounds can indeed be separated into their constituent elements through chemical reactions.

Understanding elements as fundamental building blocks of matter is crucial in chemistry, as they serve as the foundational components from which all substances are formed. The other options describe concepts that pertain to compounds or mixtures, which do not apply to the definition of an element.