2. Can a compound be made up of one atom?

• A compound is defined as a pure substance that is made up of two or more elements in a fixed ratio by mass.
• For example, water $\left({\mathrm{H}}_2\mathrm{O}\right)$ is a compound that is formed when two atoms of hydrogen $\left(\mathrm{H}\right)$ combine with one atom of oxygen $\left(\mathrm{O}\right)$.
• A compound is generally formed when two or more atoms of different elements combine chemically.

Hence, a compound cannot be made up of one atom.