Question

Which one of the cyano complexes would exhibit the lowest value of para magnetic behaviour ?
(At. No. Cr = 24, Mn = 25, Fe = 26, Co = 27)
A. `|Cr(CN)_(6)|^(3-)`
B. `|Mn(CN)_(6)|^(3-)`
C. `|Fe(CN)_(6)|^(3-)`
D. `|Co(CN)_(6)|^(3-)`

Answer 1

Correct Answer - D
Cr(III) is `d^(3)` , Mn(III) is `d^(4)`, Fe(III) is `4d^(5)`, Co(III) is `d^(6)`
`CN^(-)` is a strong ligand pairing can take place whereever required to make two empty d-orbitals available for `d^(2)sp^(3)` hybridisation.

Co(III) has no unpaired electron. Hence it is least paramagnetic.