To determine the properties of the complexes \([Ni(CO)_4]\) and \([NiCl_4]^{2-}\), we need to analyze their electronic configurations and types of bonding.
The electronic configuration of a Nickel (Ni) atom in its elemental form (atomic number 28) is:
\([Ar] \, 3d^8 \, 4s^2\)
In the formation of complexes, the oxidation state and the nature of ligands influence the electronic configuration.
\([Ni(CO)_4]\) is a complex where Ni is in the zero oxidation state. Carbon monoxide (CO) is a strong field ligand and causes the pairing of electrons in the 3d subshell.
\([NiCl_4]^{2-}\) is a complex where Ni is in the +2 oxidation state.
Based on the analysis, the correct property is:
Therefore, the correct option is: \([Ni(CO)_4]\) diamagnetic, \([NiCl_4]^{2-}\) paramagnetic.
In \([\text{Ni}(\text{CO})_4]\), nickel is in the zero oxidation state and has a \(3d^{10}\) electron configuration, leading to a fully paired electron configuration, making it diamagnetic.
In contrast, in \([\text{NiCl}_4]^{2-}\), nickel is in the \(+2\) oxidation state with a \(3d^8\) electron configuration. The chloride ligands are weak-field ligands and do not pair up the electrons, resulting in unpaired electrons and a paramagnetic nature.
Thus, the correct answer is:
\[ [\text{Ni}(\text{CO})_4] \text{ is diamagnetic and } [\text{NiCl}_4]^{2-} \text{ is paramagnetic.} \]What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)

Cobalt chloride when dissolved in water forms pink colored complex $X$ which has octahedral geometry. This solution on treating with cone $HCl$ forms deep blue complex, $\underline{Y}$ which has a $\underline{Z}$ geometry $X, Y$ and $Z$, respectively, are
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)