What does a molecule consist of?

A molecule is defined as a group of two or more atoms that are bonded together, forming the smallest identifiable unit of a chemical compound. This definition is essential because it indicates that a molecule can consist of a combination of the same type of atoms, such as in oxygen gas (O2), or different types of atoms, like in water (H2O). The atom arrangement in a molecule is what gives the substance its unique properties and characteristics, making option B the most accurate and comprehensive description.

Molecules can represent a vast array of substances, ranging from simple diatomic elements to complex organic compounds. Understanding this concept is fundamental in chemistry, as it lays the groundwork for studying chemical reactions, bonding, and molecular interactions. The other options fail to capture the broader definition of a molecule by incorrectly limiting its composition or types of constituents.