Which of the following options are correct for [Fe(CN).l3-complex?
(A) d2sp3 hybridisation
(B) sp3d2 hybridisation
(C) Paramagnetic
(D) Diamagnetic

Solution
Let the complex be [Fe(CN)6]3−.
The oxidation state of Fe can be calculated as follows:
Let the oxidation state of Fe be x.
CN​​​​​​ is a ligand which has −1 charge.
x + 6(−1) = 3−
x = +3
So, the oxidation state of Fe is 3+
It has the electronic configuration as [Ar] 3d 5.
The hybridisation scheme is as shown in diagram.


Six pairs of electrons, one from each CN molecule, occupy the six hybrid orbitals. Thus, the complex has octahedral geometry and is paramagnetic because of the presence of 1 unpaired electron1. This complex uses inner orbital (3d) in hybridisation (d2sp3).  
​​​​​​​
Hence, the correct answers are options (A) and (C).

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