Which of the following will show optical isomerism?
$I$. $\text{Cis}-[Co(NH_3)_2(en)_2]^{3+}$
$II$. $\text{Trans}-[IrCl_2(C_2O_4)_2]^{3-}$
$III$. $[Rh(en)_3]^{3+}$
$IV$. $\text{Cis}-[Ir(H_2O)_3Cl_3]$

Identify the complex compound$(s)$ which is/are optically active and whose optical activity does not depend upon the orientation of the ligands around the metal cation:
$(i). [CoCl_3(NH_3)_3]$
$(ii). [Co(en)_3]Cl_3$
$(iii). [Co(C_2O_4)_2(NH_3)_2]^-$
$(iv). [CrCl_2(NH_3)_2(en)]^+$

The metal atom present in the complex $MABXL$ (where $A, B, X$ and $L$ are unidentate ligands and $M$ is metal) involves $sp^3$ hybridization. The number of geometrical isomers exhibited by the complex is:

The $d$ electron configurations of $Cr^{2+}, Mn^{2+}, Fe^{2+}$ and $Ni^{2+}$ are $3d^4, 3d^5, 3d^6$ and $3d^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?
(At. No. $Cr = 24, Mn = 25, Fe = 26, Ni = 28$)

The electronic configurations of $Cr^{2+}$,$Mn^{2+}$,$Fe^{2+}$,and $Co^{2+}$ ions are $d^4$,$d^5$,$d^6$,and $d^7$ respectively. Which of the following complexes has the minimum paramagnetic character?

The magnetic moment of $[Fe(H_2O)_6]^{3+}$ is $5.92 \ BM$,whereas the magnetic moment of $[Fe(CN)_6]^{3-}$ is $1.74 \ BM$. Explain why.