# If which of the following order the given complex ions are arranged correctly

Question:

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) $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$

1. (ii) $>$ (i) $>$ (iii) $>$ (iv)

2. $($ iii $)>($ iv $)>($ ii $)>($ i $)$

3. (ii) $>($ iii $)>($ i $)>($ iv $)$

4. (i) $>$ (iii) $>$ (iv) $>$ (ii)

Correct Option: , 4

Solution:

$\left[\mathrm{FeF}_{6}\right]^{3-} \mathrm{Fe}^{3+} 3 \mathrm{~d}^{5} \rightarrow 5$-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