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What are the oxidation numbers of Cr in [Cr(H2O)6]Cl3, [Cr(C6H6)2], and K2[Cr(CN)2(O2)(O2)(NH3)] respectively?

1. +3, +4, and +6
2. +3, +2, and +4
3. +3, 0, and +6
4. +3, 0, and +4

Correct answer: +3, 0, and +6

Solution

The oxidation number of Cr in [Cr(H2O)6]Cl3 is +3 because the complex is neutral and the water molecules are neutral ligands. In [Cr(C6H6)2], Cr has an oxidation state of 0 since benzene is a neutral ligand and does not contribute to the charge. Finally, in K2[Cr(CN)2(O2)(O2)(NH3)], Cr is +6 as the overall charge of the complex must balance with the contributions from the ligands and the potassium ions.

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