Concept:A compound is a substance formed when two or more different elements are chemically combined in a fixed ratio.Explanation:Copper and sulphur are elements because each contains only one kind of atom.Diamond is made only of carbon atoms, so it is an elementary substance, not a compound.Sucrose (C12H22O11) contains carbon, hydrogen, and oxygen atoms joined in a definite ratio.Therefore, sucrose is the compound among the given options.Answer:Option C. Sucrose.