What kind of isomerism exists between $[Cr(H_2O)_6]Cl_3$ and $[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O$?

Assertion : $[Fe(CN)_6]^{3-}$ is weakly paramagnetic while $[Fe(CN)_6]^{4-}$ is diamagnetic.
Reason : $[Fe(CN)_6]^{3-}$ has $+3$ oxidation state while $[Fe(CN)_6]^{4-}$ has $+2$ oxidation state.

Give an example of solvate isomerism.

Match List-$I$ with List-$II$.

List-$I$ (Complex)	List-$II$ (Spin only magnetic moment in $B$.$M$.)
$A$. $[Cr(NH_3)_6]^{3+}$	$I$. $4.90$
$B$. $[NiCl_4]^{2-}$	$II$. $3.87$
$C$. $[CoF_6]^{3-}$	$III$. $0.0$
$D$. $[Ni(CN)_4]^{2-}$	$IV$. $2.83$

Choose the correct answer from the options given below:

The 'spin only' magnetic moment value of $MO_4^{2-}$ is . . . . . $BM$. (Where $M$ is a metal having least metallic radii among $Sc, Ti, V, Cr, Mn$ and $Zn$).
(Given atomic number: $Sc=21, Ti=22, V=23, Cr=24, Mn=25$ and $Zn=30$)

If $n$ is the number of unpaired electrons,then the magnetic moment $(B.M.)$ of a transition metal/ion is given by: