$A$ complex compound which can show optical isomerism but not geometrical isomerism is:

The pair having the same magnetic moment is $:$
[At. No.$: $ $Cr= 24, Mn= 25, Fe= 26, Co= 27$]

$A$ solution of $[Ni(H_{2}O)_{6}]^{2+}$ is green but a solution of $[Ni(CN)_{4}]^{2-}$ is colourless. Explain.

The total number of possible isomers for $[Pt(NH_3)_4Cl_2]Br_2$ is . . . . . . .

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.

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.