Choose the correct code regarding the possible number of geometrical isomers exhibited by the following complexes:
$I. [CrCl_2(NO_2)_2(NH_3)_2]^-$
$II. [Co(NO_2)_3(NH_3)_3]$
$III. [PtCl(NO_2)(NH_3)(py)]$
$IV. [PtBrCl(en)]$
Select the correct sequence for $I - II - III - IV$.

How many geometrical isomers are possible for the square planar complex $[Pt(NH_3)(Br)(Cl)(Py)]^{2+}$?

Among the following,the coloured compound is:

Consider the following statements and select the correct option using the codes given.
$(i)$ $[Cr(NH_3)_6][Cr(CN)_6]$ and $[Cr(NH_3)_4(CN)_2][Cr(NH_3)_2(CN)_4]$ are coordination isomers.
$(ii)$ $[Cr(py)_2(H_2O)_2Cl_2]Cl$ and $[Cr(py)_2(H_2O)Cl_3]H_2O$ are linkage isomers.
$(iii)$ $[Pt(NH_3)_4Br_2]Cl_2$ and $[Pt(NH_3)_4Cl_2]Br_2$ are linkage isomers.
$(iv)$ $[NiCl_2(PPh_3)_2]$ (tetrahedral) exhibits geometrical isomerism.

Draw the structures of optical isomers of:
$(i)$ $[Cr(C_2O_4)_3]^{3-}$
$(ii)$ $[PtCl_2(en)_2]^{2+}$
$(iii)$ $[Cr(NH_3)_2Cl_2(en)]^{+}$

The difference in the number of unpaired electrons of a metal ion in its high-spin and low-spin octahedral complexes is $2$. The metal ion is