Amongst the following the most stable complex is
(i) [Fe(H2O)6]3+
(ii) [Fe(NH3)6]3+
(iii) [Fe(C2O4)3]3-
(iv) [FeCl6]3-
Among all the complex given [Fe(C2O4)3]3- have a bidentate ligand whereas all the other three have unidentated ligand. Now we know that in chelate effect, the bidentate ligand forms a ring like structure and complex so formed is very stable with strong bond between them.
So, [Fe(C2O4)3]3- is the most stable complex.
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