In which of the following complex ions is the central metal atom's $d$-orbital devoid of electrons?

The structure of $[Cu(H_2O)_4]^{2+}$ ion is

The complex ion $[Cu(NH_3)_4]^{2+}$ has:

Geometrical shapes of the complexes formed by the reaction of $Ni^{2+}$ with $Cl^{-}$,$CN^{-}$,and $H_2O$,respectively,are

If $Ni^{2+}$ is replaced by $Pt^{2+}$ in the complex $[NiCl_2Br_2]^{2-}$,which of the following properties are expected to change?
$A.$ Geometry
$B.$ Geometrical isomerism
$C.$ Optical isomerism
$D.$ Magnetic properties

What type of geometry and magnetic nature is present in the complex $[NiCl_4]^{2-}$?