The number of unpaired electrons in $Ni(CO)_4$ is

The geometry of the $[Cu(NH_3)_4]^{2+}$ ion (tetraamminecopper$(II)$ ion) is ................ .

In which of the following configurations will there be the possibility of both paramagnetism and diamagnetism,depending on the nature of the ligands?

The pair$(s)$ of complexes wherein both exhibit tetrahedral geometry is(are):
Note: $py = \text{pyridine}$
Given: Atomic numbers of $Fe, Co, Ni$ and $Cu$ are $26, 27, 28$ and $29$,respectively.
$(A)$ $[FeCl_4]^-$ and $[Fe(CO)_4]^{2-}$
$(B)$ $[Co(CO)_4]^-$ and $[CoCl_4]^{2-}$
$(C)$ $[Ni(CO)_4]$ and $[Ni(CN)_4]^{2-}$
$(D)$ $[Cu(py)_4]^+$ and $[Cu(CN)_4]^{3-}$

Match the following hybridization in Column $I$ with the corresponding coordination complexes in Column $II$.

$A. sp^3$	$(i). [Co(NH_3)_6]^{3+}$
$B. dsp^2$	$(ii). [Ni(CO)_4]$
$C. sp^3d^2$	$(iii). [Pt(NH_3)_2Cl_2]$
$D. d^2sp^3$	$(iv). [CoF_6]^{3-}$
	$(v). [Fe(CO)_5]$

The number of unpaired electrons in $Ni(CO)_4$ is ..........