$\mu=\sqrt{15}\,BM$
${\left[ Cr \left( H _{2} O \right)_{6}\right]^{3+}}$
number of unpaired $e^{-}=3$
$\mu=\sqrt{15}\,BM$
Difference in spin only magnetic moment $=0$
$(i)$ $\left[ FeF _{6}\right]^{3-}$
$(ii)$ $\left[ Co \left( NH _{3}\right)_{6}\right]^{3+}$
$(iii)$ $\left[ NiCl _{4}\right]^{2-}$
$(iv)$ $\left[ Cu \left( NH _{3}\right)_{4}\right]^{2+}$