What best differentiates an element from a compound?

What best differentiates an element from a compound?

• A. An element is a pure substance of one type of atom; a compound is made of two or more elements chemically bonded.
• B. An element is composed of molecules; a compound is a pure atom.
• C. An element can be separated into simpler substances by physical means; a compound cannot be separated.
• D. An element has fixed composition; a compound does not.

Answer: (A)

Elements are pure substances made of only one kind of atom, which can exist as single atoms or as molecules consisting of that same atom (like O2). A compound, by contrast, is a substance formed when two or more different elements join together chemically in a fixed ratio, with the atoms held together by chemical bonds. This distinction—one type of atom in an element versus multiple elements bonded in a compound—is what best differentiates the two. It’s also why compounds can be decomposed into their elements through chemical reactions, while elements themselves cannot be broken down into simpler substances by ordinary chemical means.

Elements are pure substances made of only one kind of atom, which can exist as single atoms or as molecules consisting of that same atom (like O2). A compound, by contrast, is a substance formed when two or more different elements join together chemically in a fixed ratio, with the atoms held together by chemical bonds. This distinction—one type of atom in an element versus multiple elements bonded in a compound—is what best differentiates the two. It’s also why compounds can be decomposed into their elements through chemical reactions, while elements themselves cannot be broken down into simpler substances by ordinary chemical means.