Washington Esthetician State Board Exam 2025 – 400 Free Practice Questions to Pass the Exam

The main characteristic of a molecule is that it is formed by a chemical bond between multiple atoms. Molecules are the smallest units of a chemical compound that retain the properties of that compound. They can consist of two or more atoms bonded together, which can be the same type of atom (as in oxygen gas, O2) or different types (as in water, H2O). This definition highlights the importance of chemical bonding in the formation of molecules, distinguishing them from individual atoms or groups of atoms that don't form distinct, stable units.

In terms of the other choices, having a fixed volume pertains more to the states of matter like solids and liquids rather than the definition of a molecule. Although some molecules are made up of a single atom, such as the noble gases, this characteristic does not apply universally to all molecules. The statement that a molecule must always contain carbon is also incorrect, as there are many molecules comprised of elements other than carbon, such as water or ammonia. Thus, the ability of molecules to form through the bond of multiple atoms is the central characteristic that differentiates them within the realm of chemistry.