A water molecule is classified as which type of substance?

• A. Element
• B. Compound
• C. Mixture
• D. Solution

Answer: (B)

When classifying substances, the important idea is how things are composed and bonded. Water is a compound because it is formed by two different elements, hydrogen and oxygen, joined together by chemical bonds in a fixed ratio (two hydrogens for every one oxygen). This creates a single substance with properties distinct from either element alone, and you can’t separate the hydrogen and oxygen into their elements just by physical means.

An element would be pure hydrogen or pure oxygen—not water, since water contains two different elements. A mixture would be a combination of substances that aren’t chemically bonded, which isn’t the case for pure water. A solution is a type of homogeneous mixture where something is dissolved in something else; pure water itself isn’t a solution, though it can be the solvent in a solution.