# A complex in which central atom carries zero oxidation state is

$\begin{array}{1 1}(a)\;[CO(NH_3)_3Cl_3&(b)\;PtCl_4.2NH_3\\(c)\;Ni(CO)_4&(d)\;Na_2[Ni(CN)_4]\end{array}$

Oxidation number is the charge left on the central atom when all the bonding pairs of electrons are removed, with the charge devolved to the most electronegative atom
For $Ni(CO)_4$ , we break the $Ni−CO$ bond and we get $Ni^0 +4\times ^-C ≡ O^+$
And thus nickel has a formal oxidation state of ZERO .
A complex in which central atom carries zero oxidation state is $Ni(CO)_4$
Hence (c) is the correct answer.
answered Jan 31, 2014
edited Feb 26