Earlier the concept of equivalent weight was very common and the concentrations of the solutions were expressed in terms of normolities. The convenience was that the substances reacted in the ratio of their gram equivalents. So there was no need for writing the balanced equations to determine the amounts of the substances reacted. However, determination of equivalent weights posed difficulty in certain cases. Moreover, the equivalent weight of the same substance is not same in different reactions. For example, `KMnO_(4)` has different equivalent weight in the basic medium than in teh acidic medium. Hence, now-a-days, mole concept is more common and the concentrations of the solutions are generally expressed in terms of molarities, though some other methods like molality, molarity, mole fractions etc. are also used The equivalent mass of CuA. will be the same in CuO and `Cu_(2)O`B. will be double in `Cu_(2)O` than in `CuO`C. will be double in `CuO` than in `Cu_(2)O`D. depends on whether copper is pure or impure