# What is the chemical formula of copper oxide?

Well... you'll have to specify the oxidation state of copper. Is it $+ 1$ or $+ 2$? Is it copper(I) or copper (II)? Your pick.
Depending on your choice, it may be $\text{CuO}$ or $\text{Cu"_2"O}$... Which one is which, if oxygen in this compound, the oxide anion ${\text{O}}^{2 -}$, has an oxidation state of $- 2$?