There are four substances, a, b c and d. a and c are pure substances. they cannot be broken down into anything simpler by chemical methods. b consists of a and d, which are not chemically bonded together. d is a pure substance. we can decompose d into a and c using chemical methods. how would we classify substance a, c, and d? a: substances a and c are elements, because they are pure substances that bond together to make substance d and cannot be broken using chemical processes . substance d is a mixture, because it is a pure substance made up of a and c. b: substances a and c are compounds, because they are pure substances that bond together to make substance d and cannot be broken using chemical processes . substance d is a mixture, because it is a pure substance made up of a and c. c: substances a and c are elements, because they are pure substances that bond together to make substance d and cannot be broken using chemical processes. substance d is a compound, because it is a pure substance made up of a and c. d: substances a, c, and d, are elements. all pure substances are elements.