Which of the following complexes will exhibit optical isomerism?

Which of the following compounds is diamagnetic?

Given below are two statements:
Statement-$I$ : The number of paramagnetic species among $[CoF_6]^{3-}$, $[TiF_6]^{3-}$, $V_2O_5$ and $[Fe(CN)_6]^{3-}$ is $3$.
Statement-$II$ : $K_4[Fe(CN)_6] < K_3[Fe(CN)_6] < [Fe(H_2O)_6]SO_4 \cdot H_2O < [Fe(H_2O)_6]Cl_3$ is the correct order in terms of number of unpaired electron$(s)$ in the complexes.
In the light of the above statements, choose the correct answer from the options given below.

The complexes $[Co(NH_3)_6][Cr(CN)_6]$ and $[Cr(NH_3)_6][Co(CN)_6]$ are the examples of which type of isomerism?

Which of the following complexes exists as a pair of enantiomers?

Which one of the following complexes is not expected to exhibit isomerism?