Amongst the following identify the species with an atom in oxidation state : `CrO_(2)Cl_(2), MnO_(4)^(-), Cr(CN)_(6)^(3-), NiF_(6)^(2-)`

Explanation

(i) In an ion sum of oxidation states of all atoms is equal to charge on ion and in a compound sum of oxidation states of all atoms is always zero.
Oxidation state of Mn in `MnO_(4)^(-) = +7`
Oxidation state of Cr in `Cr(CN)_(6)^(3-) = +3`
Oxidation state of Ni in `NiF_(6)^(2-) = +4`
Oxidation state of Cr in `CrO_(2)Cl_(2) = +6`