Question

Arrange the following in order of decreasing number of unpaired electrons?
I. ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+}$
II. ${\left[Fe(CN{)}_6\right]}^{3-}$
III. ${\left[Fe(CN{)}_6\right]}^{4-}$
IV. ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{3+}$

• A. IV, I, II, III
• B. I, II, III, IV
• C. III, II, I, IV
• D. II, III, I, IV

Answer 1

Answer: (A)

(i) ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+},3d^6$



$n=4$ (weak field ligand)

(ii) ${\left[Fe(CN{)}_6\right]}^{3-},3d^5$



$n=1$ (Strong field ligand)

(iii) ${\left[Fe(CN{)}_6\right]}^{4-},3d^6$



$n=0$ (strong field ligand)

(iv) ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{3-},3d^5$



$n=5$ (weak field ligand)