Which of the following best describes the difference between a molecule and an atom, and provides a correct example?

• A. A molecule is a single atom of a noble gas, such as He, while an atom is a combination of molecules.
• B. A molecule is a group of atoms held together by physical forces, such as NaCl, while an atom is a group of protons and neutrons.
• C. A molecule consists of two or more atoms chemically bonded together, such as H2O, while an atom is a single unit of an element, such as O.
• D. A molecule is a single atom with a positive charge, such as Na+, while an atom is always neutral, such as Na.

Answer: (C)

Verified step by step guidance

1. Understand the definition of an atom: An atom is the smallest unit of an element that retains the chemical properties of that element. It consists of protons, neutrons, and electrons.
2. Understand the definition of a molecule: A molecule is formed when two or more atoms chemically bond together. These atoms can be the same or different elements.
3. Evaluate the examples given: For an atom, a single element like oxygen (O) is a good example. For a molecule, water (H2O) is a classic example because it consists of two hydrogen atoms and one oxygen atom bonded together.
4. Analyze the incorrect options: For example, NaCl is an ionic compound, not a molecule held by physical forces; Na+ is an ion, not a molecule; and a noble gas like He is a single atom, not a molecule.
5. Conclude that the correct description is: A molecule consists of two or more atoms chemically bonded together, such as H2O, while an atom is a single unit of an element, such as O.