# Question #e5065

You mean, what is the oxidation number of Co in $K \left[C o {\left(C O\right)}_{4}\right]$?
Therefore, the complex can be written as ${K}^{+} {\left[C o {\left(C O\right)}_{4}\right]}^{-}$, Therefore, the oxidation number of Co in the given complex is -1.