What term describes the smallest stable unit of a substance that retains its chemical properties?

• A. Molecule
• B. Molecular Compound
• C. Chemical Formula
• D. Bond Energy

Answer: (A)

Understanding what makes up a substance starts with the idea of discrete units that retain its chemical behavior. A molecule is the smallest stable group of atoms bonded together that still behaves as the substance. For covalent substances, this unit carries the characteristic properties of the substance, so water’s properties come from water molecules (H2O). If you break a molecule into separate atoms, you don’t have the same substance anymore, because the defining properties arise from the bonded arrangement.

A chemical formula simply shows the types and numbers of atoms present; it doesn’t describe a unit that itself preserves the substance’s properties. Bond energy is about the strength of a bond, not about a unit of matter. A molecular compound refers to a substance composed of molecules, but the term describes the type of substance rather than the smallest unit that carries its properties.