# Cobalt, a transition metal, can have an oxidation number of either 2+ or 3+. What are the two possible chemical formula for the chemical combination of cobalt with oxygen?

Well, there is $\text{cobalt(II) oxide}$, $C o O$.....$\text{cobaltous oxide}$
And $\text{cobalt(III) oxide}$, $C {o}_{2} {O}_{3}$.....$\text{cobaltic oxide}$.
And a mixed oxidation state oxide exists, $C {o}_{3} {O}_{4}$ (note that I simply added the given formulae together, $\text{cobalt(II,III) oxide}$).