The number of possible geometric isomers for a square planar complex $[Mabcd]$ is ............. ($M =$ central metal,$a, b, c, d =$ monodentate ligands).

Consider the following isomerisms:
$1.$ Ionization
$2.$ Hydrate
$3.$ Linkage
$4.$ Geometrical
$5.$ Optical
Which isomerisms are exhibited by $[Cr(NH_3)_2(OH)_2Cl_2]^-$?

Which of the following pairs of isomers and their types of isomerism are correctly matched?
$1.$ $[Co(NH_3)_5NO_2]Cl_2$ and $[Co(NH_3)_5ONO]Cl_2$ $-$ Linkage
$2.$ $[Cu(NH_3)_4] [PtCl_4]$ and $[Pt(NH_3)_4] [CuCl_4]$ $-$ Coordination
$3.$ $[Pt(NH_3)_4Cl_2]Br_2$ and $[Pt(NH_3)_4Br_2]Cl_2$ $-$ Ionization

Number of complexes from the following with an even number of unpaired $d$ electrons is . . . . . . . . . .
$[V(H_2O)_6]^{3+}, \quad [Cr(H_2O)_6]^{2+}, \quad [Fe(H_2O)_6]^{3+}, \quad [Ni(H_2O)_6]^{3+}, \quad [Cu(H_2O)_6]^{2+}$
[Given atomic numbers: $V=23, Cr=24, Fe=26, Ni=28, Cu=29$]

Which of the following compounds shows optical isomerism?

What will be the theoretical value of magnetic moment $(\mu)$ when $CN^-$ ligands join $Fe^{3+}$ ion to yield a complex (in $BM$)?