To determine the magnetic properties of the complexes \(\text{[Ni(CO)}_4\text{]}\) and \(\text{[NiCl}_4\text{]}^{2-}\), we need to consider the following:
- \(\text{[Ni(CO)}_4\text{]}\):
- Nickel in its zero oxidation state is given in this complex. The electronic configuration of Ni is \(\text{[Ar]} \, 3d^{8} \, 4s^{2}\).
- CO is a strong field ligand and causes the pairing of electrons. The electrons from the 3d orbitals pair up and thus all the 3d orbitals get filled with paired electrons.
- After pairing, the 3d orbitals are completely filled, leading to no unpaired electrons in the Ni 3d subshell.
- Therefore, \(\text{[Ni(CO)}_4\text{]}\) is diamagnetic.
- \(\text{[NiCl}_4\text{]}^{2-}\):
- Nickel in this complex is in a +2 oxidation state. Thus, the electronic configuration is \(\text{[Ar]} \, 3d^{8}\).
- Cl is a weak field ligand and doesn't cause pairing of electrons.
- As a result, Ni retains unpaired electrons in its d orbitals.
- This implies that \(\text{[NiCl}_4\text{]}^{2-}\) is paramagnetic due to the presence of unpaired electrons.
The correct property for the given options is:
- \(\text{[Ni(CO)}_4\text{]}\) is diamagnetic because it has no unpaired electrons.
- \(\text{[NiCl}_4\text{]}^{2-}\) is paramagnetic due to the presence of unpaired electrons.
Therefore, the correct option is: \( \text{[Ni(CO)}_4\text{]} \) diamagnetic, \( \text{[NiCl}_4\text{]}^{2-} \) paramagnetic.