A 분자 (Molecule) is the smallest unit of a chemical compound that retains its chemical properties. It consists of two or more atoms that are bonded together, which can be the same or different elements. For example, a water molecule (H₂O) is made up of two hydrogen atoms and one oxygen atom. Molecules can vary in size and complexity, ranging from simple diatomic molecules like O₂ (oxygen) to large biological molecules like DNA. They play a crucial role in chemistry and biology, as they are the building blocks of matter and are involved in various chemical reactions.