Question

In which of the following complex the nickel metal is in highest oxidation state?

• A. $Ni(CO{)}_4$
• B. $K_{2}Ni{F}_6$
• C. $\left[Ni{\left(N{H}_3\right)}_6\right]{\left(B{F}_4\right)}_2$
• D. $K_4\left[Ni(CN{)}_6\right]$

Answer 1

Answer: (B)

$\left[Ni(CO{)}_4\right]$ carbonyl is a neutral ligand. So the oxidation state of nickel is $O$.
$K_2\left[Ni{F}_6\right]$ fluoro is anionic ligand with $-1$ charge. So the oxidation state of nickel is $+4$.
$\left[Ni{\left(N{H}_3\right)}_6\right]{\left(B{F}_4\right)}_2$ ammine is neutral ligand and $B{F}_4$ has $-1$ charge. So the oxidation state of nickel is $+2$.
$K_4\left[Ni(CN{)}_6\right]$ cyano is anionic ligand with charge $-1$. So the oxidation state of nickel is $+2$.