Transition elements are able to show variable oxidation states. Which pair of compounds shows a transition element in two different oxidation states?
- A$\text{Cr}_2\text{O}_3$ and $\text{Cr}_2(\text{SO}_4)_3$
- B$\text{Cu}_2\text{O}$ and $\text{CuCO}_3$
- C$\text{ZnS}$ and $\text{ZnSO}_4$
- D$\text{NiO}$ and $\text{Ni(NO}_3)_2$