The spin-only magnetic moment value of an octahedral complex among CoCl 3 · 4 NH 3 , NiCl 2 · 6 H…

(I) ${\mathrm{H}}_2\left[{\mathrm{PtCl}}_6\right]\to$ no ppt with ${\mathrm{AgNO}}_3$

${\mathrm{Pt}}^{+4}, \mathrm{CN}=6$

(II) $\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\mathrm{Cl}}_2 \frac{{\mathrm{AgNO}}_3}{\mathrm{excess}} 2$ mole of $\mathrm{AgCl}\downarrow$,

${\mathrm{Ni}}^{+2},\mathrm{CN}=6,\mathrm{n}=2, {\mathrm{\mu }}_{\mathrm{m}}=\sqrt{\mathrm{n}\left(\mathrm{n}+2\right)} \mathrm{BM}=\sqrt{8}=2.82\mathrm{BM}\simeq 3$

Aqua complexes, generally have $\mathrm{CN}=6$

(III) $\left[{\mathrm{CoCl}}_2{\left({\mathrm{NH}}_3\right)}_4\right]\mathrm{Cl}\underset{\mathrm{excess}}{\stackrel{{\mathrm{AgNO}}_3}{⟶}}1$ Mole of $\mathrm{AgCl}\downarrow$,

${\mathrm{Co}}^{+3},\mathrm{CN}=6$