Which of the following best describes an element?

• A. A substance composed of molecules containing different types of atoms.
• B. A mixture of two or more different atoms.
• C. A compound formed from two or more elements.
• D. A substance that cannot be broken down into simpler substances by chemical means.

Answer: (D)

Verified step by step guidance

1. Understand the definition of an element in chemistry: An element is a pure substance consisting of only one type of atom.
2. Recognize that an element cannot be broken down into simpler substances by chemical means because it is the simplest form of matter with unique properties.
3. Differentiate an element from a compound, which is a substance formed from two or more different elements chemically combined.
4. Distinguish an element from a mixture, which contains two or more substances physically combined but not chemically bonded.
5. Conclude that the best description of an element is: 'A substance that cannot be broken down into simpler substances by chemical means.'