Which one of the following complexes will have four isomers?

For a metal ion,the calculated magnetic moment is $4.90 \ BM$. This metal ion has $........$ number of unpaired electrons.

Among the following complexes,the total number of diamagnetic species is. . . . $[Mn(NH_3)_6]^{3+}, [MnCl_6]^{3-}, [FeF_6]^{3-}, [CoF_6]^{3-}, [Fe(NH_3)_6]^{3+}$ and $[Co(en)_3]^{3+}$
[Given,atomic number: $Mn=25, Fe=26, Co=27$; $en=H_2NCH_2CH_2NH_2$ ]

Calculate the magnetic moment of the $Fe^{3+}$ ion in the $[Fe(CN)_6]^{3-}$ complex.

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:

Which of the following compounds has the highest magnetic moment?