Which of the following compounds is paramagnetic and colored?

Other than $X$-ray diffraction,how can the following pairs of isomers be distinguished from one another?
$[Cr(NH_3)_6][Cr(NO_2)_6]$ and $[Cr(NH_3)_4(NO_2)_2][Cr(NH_3)_2(NO_2)_4]$

Which of the following complexes can show coordination isomerism?

The atomic numbers of $Cr$ and $Fe$ are $24$ and $26$ respectively. Which of the following is paramagnetic in terms of electron spin?

Total number of unpaired electrons present in the central metal atoms/ions of $[Ni(CO)_{4}]$, $[NiCl_{4}]^{2-}$, $[PtCl_{2}(NH_{3})_{2}]$, $[Ni(CN)_{4}]^{2-}$ and $[Pt(CN)_{4}]^{2-}$ is . . . . . . .

Select the correct statement about the given square planar complex.