The difference between spin only magnetic moment values of Co H 2 O 6 Cl 2 and Cr H 2 O 6 Cl 3 is

${\left[\mathrm{Co}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$

Number of unpaired ${\mathrm{e}}^{-}=3$

$$\begin{gathered} \mathrm{\mu }=\sqrt{\mathrm{n}\left(\mathrm{n}+2\right)}\mathrm{BM} \\ \mathrm{n}=\mathrm{number} \mathrm{of} \mathrm{unpaired} \mathrm{electrons} \end{gathered}$$

$\mathrm{\mu }=\sqrt{15}\mathrm{BM}$

${\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$

number of unpaired ${\mathrm{e}}^{-}=3$

$\mathrm{\mu }=\sqrt{15}\mathrm{BM}$

Difference in spin only magnetic moment $=0$