Amongst the following, identify the species with an atom in +6 oxidation state:

$\left[\mathrm{MnO}_{4}\right]^{-}$

$\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{3-}$

$\mathrm{Cr}_{2} \mathrm{O}_{3}$

$\mathrm{CrO}_{2} \mathrm{Cl}_{2}$