Which one of the following has the largest number of isomers?
($R$ = alkyl group; $en$ = ethylenediamine)

Which complex is likely to show optical activity?

Arrange the following coordination compounds in the increasing order of magnetic moments. (Atomic numbers: $Mn = 25$; $Fe = 26$)
$(A)$ $[FeF_{6}]^{3-}$
$(B)$ $[Fe(CN)_{6}]^{3-}$
$(C)$ $[MnCl_{6}]^{3-}$ (high spin)
$(D)$ $[Mn(CN)_{6}]^{3-}$

Arrange the following in the increasing order of their magnetic moments:
$I.$ $[Mn(CN)_6]^{3-}$
$II.$ $[MnCl_6]^{3-}$
$III.$ $[Fe(CN)_6]^{3-}$
$IV.$ $[FeF_6]^{3-}$

Identify the metal ions among $Co^{2+}, Ni^{2+}, Fe^{2+}, V^{3+}$ and $Ti^{2+}$ having a spin-only magnetic moment value more than $3.0 \ BM$. The sum of unpaired electrons present in the high spin octahedral complexes formed by those metal ions is . . . . . . .

The most paramagnetic complex is