what is the oxidation state of Co atom in [Co(DMH)2ClPy]?

Each DMH⁻ ligand (5,5-dimethylhydantoin ligand) carries a charge of -1.
Hence, the sum of oxidation states of a DMH⁻ ligand = -1

Each Cl⁻ ligand also carries a charge of -1.
Hence, the oxidation state of Cl in a Cl⁻ ligand = -1

Py ligand (pyridine ligand) is neutral in charge.
Hence, the sum of oxidations states of a Py ligand = 0

[Co(DMH)₂ClPy] is a neutral complex.
Hence, sum of oxidation states = 0
(Oxidation state of Co) + (-1)×2 + (-1)×1 + (0)×1 = 0
Hence, oxidation state of Co = +3

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