What term is used for substances that can be broken down into simpler substances?

Compounds are substances formed when two or more elements chemically combine in fixed ratios. This means that they can be decomposed into simpler substances—specifically, their elemental components—through chemical reactions. For example, water (H2O) is a compound made from hydrogen and oxygen; it can be broken down into these two elements through electrolysis.

In contrast, elements are the most basic form of matter and cannot be broken down into simpler substances. Mixtures consist of two or more substances that are physically combined but not chemically bonded, allowing for separation without chemical changes. Solutions are a specific type of mixture where one substance (the solute) is dissolved in another (the solvent), but like mixtures, they do not involve chemical bonding between the constituents. Therefore, compounds are uniquely defined by their ability to be broken down into simpler substances, which makes this term the correct answer.