Question

How many oxygen atoms in blue per chromate $\left({CrO}_5\right)$ are having $-1$ oxidation state?

Answer 1

In the structure of ${CrO}_5$, there is no oxygen double bonded to the $Cr$ atom and there are two peroxide linkages $(-O-O-)$.

Four oxygen atoms of two peroxide linkages have $-1$ oxidation state.