Which statement best describes a compound?

• A. A compound is a substance that cannot be broken down into simpler substances by chemical means.
• B. A compound is a mixture of two or more substances that can be separated by physical means.
• C. A compound consists of only one type of atom.
• D. A compound is a substance composed of two or more elements chemically combined in a fixed ratio.

Answer: (D)

Verified step by step guidance

1. Understand the definition of a compound: A compound is a substance formed when two or more elements are chemically combined in a fixed ratio.
2. Recognize that compounds have distinct properties different from the elements that compose them, and they can be broken down into simpler substances (elements) by chemical means.
3. Distinguish compounds from mixtures: Mixtures contain two or more substances physically combined and can be separated by physical means, whereas compounds cannot.
4. Note that a compound is not made of only one type of atom; that description fits an element.
5. Conclude that the best description of a compound is that it is a substance composed of two or more elements chemically combined in a fixed ratio.