Question

Give the oxidation number and coordination number of the central metal atom in the complex compound $K_3\left[Fe\right(C_2{O}_4{)}_3]$.

Answer 1

The central atom in the complex $K_3\left[Fe\right(C_2{O}_4{)}_3]$ is Fe. Its coordination number is 6. It is attached to three oxalate ligands Oxalate is a bidentate ligand.
The oxidation number of $Fe$ is $+3$. Each oxalate ligand has oxidation number of $-2$ and each potassium ion has oxidation number of $+1$. Let $X$ be the oxidation number of Fe.
$3(+1)+X+3(-2)=0$
$X=+3$