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Question:

Which of the following complex compounds will exhibit highest paramagnetic behaviour?

[Ti(NH3)6]3+

[Co(NH3)6]3+

[Cr(NH3)6]3+

[Zn(NH3)6]2+

Solution:

(A)[Ti(NH3)6]3+: Ti has 3d1 configuration and thus has one unpaired electron
(B)[Cr(NH3)6]3+: The complex is inner orbital complex but 3d3 configuration has three unpaired electrons with weak as well as with strong field ligand
(C)[Co(NH3)6]3+: The cobalt ion is in +3 oxidation state with 3d6 configuration and thus is diamagnetic octahedral complex, [Co(NH3)6]3+, as the electrons paired up
(D)[Zn(NH3)6]2+: Because of 3d10 configuration no d orbital is available for d2sp3 hybridisation and thus forms outer orbital complex. The complex is diamagnetic.