What is the oxidation number of the metal of $[\text{Co}(\text{H}_2\text{O})(\text{CN})(\text{ox})_2]^{2-}$ coordination entity?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → +3
Oxidation state of the central metal is calculated by considering the charges of all ligands and the overall charge of the complex.
Neutral ligands contribute 0 charge, while anionic ligands contribute their respective negative charges.
Let oxidation state of $\text{Co} = x$
Ligand charges:
$\text{H}_2\text{O}$ is neutral $\rightarrow 0$
$\text{CN}^- \rightarrow -1$
Oxalate $(\text{ox}^{2-}) \rightarrow -2$ each
Since there are two oxalate ligands:
Total ligand charge =
$\text{CN}^- = -1$
$2 \times \text{ox}^{2-} = -4$
Total ligand charge $= -5$
Overall charge of complex $= -2$
So,
$x + (-5) = -2$
$x = +3$