Radiation Safety Practice Exam

Which of the following is the smallest unit of a compound still retaining its unique physical and chemical characteristics?

1. Atom

2. Cell

3. Molecule

4. Substance

The correct answer is: Molecule

The smallest unit of a compound that still retains its unique physical and chemical characteristics is a molecule. A molecule consists of two or more atoms that are chemically bonded together, which results in distinct properties that are specific to that compound. This means that the individual properties of the atoms that compose the molecule may differ from the properties of the molecule itself. In the context of compounds, when two or more atoms join together to form a molecule, they create a new entity that has its own unique behavior and characteristics. For instance, water (H2O) is a molecule made up of hydrogen and oxygen atoms, and it exhibits properties that are quite different from the individual gases that compose it. While an atom is smaller than a molecule and represents the basic building block of matter, it does not represent a compound on its own. A cell, which is a biological unit, is much larger and consists of various molecules. A substance refers to a form of matter with a specific composition and distinct properties but does not denote the smallest unit that carries those characteristics. Therefore, the concept of a molecule is essential in defining the smallest unit of a compound that retains its specific properties.