Question

which statement correctly explains the difference between an atom and a molecule?

• an atom is a single particle of a substance, while a molecule is a combination of two or more atoms bonded together.
• an atom can be broken down into smaller parts, but a molecule cannot.
• an atom is the smallest unit of a compound, while a molecule is the smallest unit of an element.
• an atom always contains more than one type of element, while a molecule contains only one type of element.

Explanation:

Define atoms and molecules

An atom is the basic building block of chemistry and the smallest unit of an element. A molecule is formed when two or more atoms chemically bond together.

Evaluate the first statement

The first statement says: "An atom is a single particle of a substance, while a molecule is a combination of two or more atoms bonded together." This correctly describes an atom as a single unit and a molecule as a bonded group of atoms.

Evaluate the second statement

The second statement says: "An atom can be broken down into smaller parts, but a molecule cannot." This is incorrect because molecules can be broken down into their constituent atoms via chemical reactions, whereas atoms cannot be broken down by chemical means.

Evaluate the third statement

The third statement says: "An atom is the smallest unit of a compound, while a molecule is the smallest unit of an element." This is incorrect; an atom is the smallest unit of an element, and a molecule is the smallest unit of a covalent compound.

Evaluate the fourth statement

The fourth statement says: "An atom always contains more than one type of element, while a molecule contains only one type of element." This is incorrect; an atom represents a single element, while molecules can contain multiple types of elements (compounds).

Answer:

• (A) An atom is a single particle of a substance, while a molecule is a combination of two or more atoms bonded together. (Correct answer)
• (B) An atom can be broken down into smaller parts, but a molecule cannot.
• (C) An atom is the smallest unit of a compound, while a molecule is the smallest unit of an element.
• (D) An atom always contains more than one type of element, while a molecule contains only one type of element.