Identify the outer orbital octahedral complexes among the following that have the same number of unpaired electrons:
(Atomic numbers of Mn, Fe, Co, and Ni are 25, 26, 27, and 28 respectively)

(a) MnCl63- (b) FeF63-
(c) CoF63- (d) NiNH362+


1. (a, b)
2. (b, c)
3. (c, d)
4. (a, c)

Molecular orbital electronic configuration of Mn3+in MnCl63- is

Number of unpaired electrons =4

Magnetic property = Paramagnetic

Molecular orbital electronic configuration of Co3+in CoF63- is

Number of unpaired electrons =4

Magnetic property = Paramagnetic

Molecular orbital electronic configuration of Fe3+in FeF63- is 

Number of unpaired electrons =4

Magnetic property = Paramagnetic

Molecular orbital electronic configuration of Ni2+ in NiNH362+ is 

Number of unpaired electrons =4

Magnetic property = Paramagnetic

Thus, MnCl63- and CoF63- are paramagnetic having four electrons each. 

Hence, correct choices are (a) (c).