Which term describes a pure substance made of only one kind of atom?

• A. Pure substance
• B. Solution
• C. Element
• D. Mixture

Answer: (C)

You’re being tested on how pure substances are defined by what their building blocks are. An element is a pure substance that contains only one kind of atom. That means everything in the substance is built from the same type of atom, even if those atoms bond together to form molecules (for example, O2 or N2 are still just oxygen or nitrogen molecules). Because it’s composed of a single kind of atom, it’s not a compound.

A compound, in contrast, contains two or more different kinds of atoms bonded together (like water, which has hydrogen and oxygen). A solution is a homogeneous mixture of substances, not a pure substance on its own. So the term for a pure substance made of only one kind of atom is element.