Which term describes a substance that cannot be broken down into simpler substances by chemical means?

• A. Element
• B. Compound
• C. Mixture
• D. Molecule

Answer: (A)

Elements are the fundamental substances that cannot be broken down into simpler substances by chemical means. Each element is made of one type of atom (defined by its number of protons), so chemical reactions can’t divide it into other substances. In contrast, compounds are formed from two or more elements bonded together and can be decomposed into those elements by chemical processes (like electrolysis for water into hydrogen and oxygen). Mixtures are just physical combinations of substances that aren’t chemically bonded, so they can be separated by physical methods. A molecule is a group of atoms bonded together; it can be two or more atoms of the same element (like O2) or different elements (like H2O). Since the question describes a substance that cannot be broken down into simpler substances by chemical means, the correct term is element.