Which one of the following complexes exhibits chirality?

The increasing order of magnetic moments for the following complexes is:
$I$. $[Fe(CN)_6]^{4-}$
$II$. $[Fe(CN)_6]^{3-}$
$III$. $[Cr(NH_3)_6]^{3+}$
$IV$. $[Ni(H_2O)_4]^{2+}$

How many optical isomers are possible for the complex $[Pt(NH_3)_2(CN)_2]$?

Which one of the following pairs of isomers and types of isomerism are correctly matched?
$(i).$ $[Co(NH_3)_5(NO_2)]Cl_2$ and $[Co(NH_3)_5(ONO)]Cl_2$ .... (Linkage)
$(ii).$ $[Cu(NH_3)_4][PtCl_4]$ and $[Pt(NH_3)_4][CuCl_4]$ .... (Coordination)
$(iii).$ $[PtCl_2(NH_3)_4]Br_2$ and $[PtBr_2(NH_3)_4]Cl_2$ .... (Ionization)
Select the correct answer using the codes given below.

Which of the following complexes can exhibit facial $(fac)$ and meridional $(mer)$ isomerism?

$A$ magnetic moment of $1.73 \ BM$ will be shown by which of the following?