Which of the following correctly describes a compound? (4 points) a The atoms are bonded together, and the compound has different physical and chemical properties than the individual elements. b The atoms have no set ratio for how the atoms can combine, and they are not chemically bonded together. c The atoms can only combine in fixed ratios, and they retain their individual chemical and physical properties. d The atoms retain their individual chemical properties, and they can only be separated from each other by a chemical change.