The smallest unit of a compound that retains the chemical properties of that compound.

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

Answer: (A)

The main idea here is that a compound’s characteristic behavior comes from how its atoms are bonded in its smallest intact form. That smallest unit is a molecule—the group of atoms held together in a specific arrangement and proportion that gives the compound its properties. If you break the molecule apart into separate atoms, you lose those properties because the bonding pattern and overall structure responsible for the compound’s behavior are no longer present.

Atoms are the building blocks of elements, not compounds, and elements by themselves don’t exhibit the combined properties of a compound. For example, water’s unique properties arise from the two hydrogen atoms and one oxygen atom arranged in a water molecule with its specific bonds and geometry. Thus, the molecule is the smallest unit that retains the chemical properties of the compound.