The atomic numbers of $Cr$ and $Fe$ are $24$ and $26$ respectively. Which of the following is paramagnetic in terms of electron spin?

Which of the following complexes exhibits both geometrical and optical isomerism?

The one that will show optical activity is: $(en = \text{ethane-}1,2\text{-diamine})$

Arrange the following complexes in the increasing order of their spin only magnetic moment (in $B.M$):
$I$. $[Fe(CN)_6]^{4-}$
$II$. $[MnCl_4]^{2-}$
$III$. $[Mn(CN)_6]^{4-}$
$IV$. $[Cr(NH_3)_6]^{3+}$

In which of the following orders are the given complex ions arranged correctly with respect to their decreasing spin-only magnetic moment?
$(i)$ $[FeF_{6}]^{3-}$
$(ii)$ $[Co(NH_{3})_{6}]^{3+}$
$(iii)$ $[NiCl_{4}]^{2-}$
$(iv)$ $[Cu(NH_{3})_{4}]^{2+}$

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: $Mn=25, Fe=26, Co=27$; $en=H_2NCH_2CH_2NH_2$ ]