If which of the following order the given complex ions are arranged correctly
If which of the following order the given complex ions are arranged correctly with respect to their decreasing spin only magnetic moment?
(i) $\left[\mathrm{FeF}_{6}\right]^{3-}$
(ii) $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$
(iii) $\left[\mathrm{NiCl}_{4}\right]^{2-}$
(iv) $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$
Correct Option: , 4
$\left[\mathrm{FeF}_{6}\right]^{3-} \mathrm{Fe}^{3+} 3 \mathrm{~d}^{5} \rightarrow 5$-unpaired electrons as $\mathrm{F}^{-}$is weal field legend
$\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+} \mathrm{Co}^{3+} 3 \mathrm{~d}^{6} \rightarrow$ No-unpaired electron as $\mathrm{NH}_{3}$ is strong field light and causes pairing
$=[\mathrm{NiCl} 4]^{2-} \mathrm{Ni}^{2+} 3 \mathrm{~d}^{8} \rightarrow 2$-unpaired electrons
$\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+} \mathrm{Cu}^{2+} 3 \mathrm{~d}^{9} \rightarrow 1$-unpaired electrons