Final answer:
A pure substance that can be broken down by chemical means is a compound. Elements are simple substances that cannot be chemically broken down, while compounds are composed of two or more elements and can be broken down into those elements.
Step-by-step explanation:
A pure substance that can be broken down by chemical changes is known as a compound. Elements, compounds, and mixtures are all classifications of matter. An element is a pure substance that cannot be broken down into simpler substances by chemical means. Examples of elements include aluminum, oxygen, and gold. In contrast, a compound is made up of two or more elements that are chemically combined in fixed proportions, such as water (H2O), which is composed of hydrogen and oxygen. Therefore, a compound can be separated into its constituent elements through chemical changes. Mixtures, however, consist of two or more substances that are not chemically bonded and can often be separated by physical means.