Explain the formation of ${\left[\mathrm{Co}\left({\mathrm{F}}_6\right)\right]}^{3-}$ according to valence bond theory.

Among the complexes of Ni listed below, the following is the only correct statement

I - $\left[\mathrm{Ni}(\mathrm{CO}{)}_4\right]$

II - ${\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{-2}$

III - ${\left[\mathrm{Ni}\left({\mathrm{Cl}}_4\right)\right]}^{-2}$

Arrange the following metal complex/ compounds in the increasing order of spin only magnetic moment. Presume all the three, high spin system.

(Atomic numbers $\mathrm{Ce}=58, \mathrm{Gd}=64$ and $\mathrm{Eu}=63$.)

(a) ${\left({\mathrm{NH}}_4\right)}_2\left[\mathrm{Ce}{\left({\mathrm{NO}}_3\right)}_6\right]$

(b) $\mathrm{Gd}{\left({\mathrm{NO}}_3\right)}_3$ and

(c) $\mathrm{Eu}{\left({\mathrm{NO}}_3\right)}_3$