Which of the following complex ions is not expected to absorb visible light?

For the octahedral complexes of $Fe^{3+}$ in $SCN^{-}$ (thiocyanato-$S$) and in $CN^{-}$ ligand environments,the difference between the spin-only magnetic moments in Bohr magnetons (when approximated to the nearest integer) is
[Atomic number of $Fe = 26$]

The following complexes are given:
$1$. $\text{trans}-[Co(NH_3)_4Cl_2]^+$
$2$. $\text{cis}-[Co(NH_3)_2(en)_2]^{3+}$
$3$. $\text{trans}-[Co(NH_3)_2(en)_2]^{3+}$
$4$. $[NiCl_4]^{2-}$
$5$. $[TiF_6]^{2-}$
$6$. $[CoF_6]^{3-}$
Choose the correct code:

The total number of possible isomers for the coordination compound $[Cu^{II}(NH_3)_4][Pt^{II}Cl_4]$ is.....

The experimental value of the magnetic moment of a $Mn^{2+}$ complex salt is $5.96 \ BM$. This indicates that ......

$CoSO_{4}Cl \cdot 5NH_{3}$ exists in two isomeric forms '$A$' and '$B$'. Isomer '$A$' reacts with $AgNO_{3}$ to give white precipitate,but does not react with $BaCl_{2}$. Isomer '$B$' gives white precipitate with $BaCl_{2}$ but does not react with $AgNO_{3}$. Answer the following questions.
$(i)$ Identify '$A$' and '$B$' and write their structural formulas.
$(ii)$ Name the type of isomerism involved.
$(iii)$ Give the $IUPAC$ name of '$A$' and '$B$.'