\(x+4(0)=0 \)
\(x=0\)
The electronic configuration of \(Ni\) is \([ Ar ] 3 d ^{8} 4 s ^{2} 4 p ^{0} .\) The orbital diagram of nickel in the presence of strong filed ligand \(CO\) is shown below.
As no unpaired electron is present in this complex, so it is diamagnetic.