Final answer:
Water (H2O) is an example of a compound; it is a pure substance made up of two hydrogen atoms and one oxygen atom, which distinguishes it from elements like hydrogen and oxygen.
Step-by-step explanation:
The example of a compound from the given choices is B) water. Compounds are pure substances comprised of two or more elements chemically combined in a fixed ratio. Water, with the chemical formula H₂O, always consists of two hydrogen atoms and one oxygen atom. Unlike elements like hydrogen (H₂) and oxygen (O₂), which consist of only one type of atom bonded together, water is a compound because it contains different types of atoms. Other examples of compounds include carbon dioxide (CO₂) and sodium chloride (NaCl).