A molecule is defined as:

• A. A single atom
• B. A group of atoms chemically bonded together
• C. A positively charged particle
• D. A nucleus with electrons

Answer: (B)

A molecule is a group of atoms chemically bonded together. This means two or more atoms join and share or transfer electrons to form a single unit with its own properties. A single atom is not a molecule; it’s just an individual atom. A positively charged particle describes an ion, not the general idea of a molecule. A nucleus with electrons describes an atom as well, since molecules are built from multiple bonded atoms, not from a single atom’s structure. For example, water (H2O) is a molecule formed from two hydrogen atoms bonded to one oxygen atom, and oxygen gas (O2) is a molecule made of two oxygen atoms bonded together.