Final answer:
A compound is a unique substance consisting of two or more elements in fixed proportions, while a molecule is the smallest part of a substance that has its properties. Molecules can exist as discrete units in molecular compounds.
Step-by-step explanation:
A compound is a unique substance that consists of two or more elements combined in fixed proportions. The composition of a compound is always the same. The smallest particle of most compounds in living things is called a molecule.
A molecule, on the other hand, is the smallest part of a substance that has the physical and chemical properties of that substance. It is composed of two or more atoms chemically bonded together. Molecules can exist as discrete units, like in molecular compounds such as water (H₂O) and carbon dioxide (CO₂).