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A coordination complex consists of a central metal atom or ion bonded to ligands by coordinate covalent bonds. The ligands and the central metal together form the coordination sphere.
In , coordination sphere consists of 2 chloro ligands with charge of -1 each and ammine ligands with zero charge. The coordination sphere carries no charge as the the coordination compound is electrically neutral.
Let the oxidation state of Pt = x
∴ x +2(-1)+2(0) = 0
Learn more about oxidation states