What is the definition of a molecule?

A molecule is defined as the smallest particle in a chemical element or compound that retains the chemical properties of that element or compound. This means that a molecule consists of two or more atoms that are bonded together, and it represents the fundamental building block of chemical substances. For instance, a water molecule is made up of two hydrogen atoms and one oxygen atom, and it has distinctive properties such as being a liquid at room temperature, which are characteristic of water.

The other options do not accurately reflect the definition of a molecule. While the smallest unit of matter might seem related, it is broader and does not specifically define a molecule, which is specifically about atoms and their bonds. Similarly, the idea of the largest particle or a unit of temperature does not align with the definition of a molecule, as molecules pertain to chemical structures rather than size or thermal measurement. Therefore, the definition aligns with the understanding of molecules as essential components of chemical identity.