Complex [Co(en)3]Cl2 is most stable complex
among the given complex compounds because
more number of chelate rings are present in this complex as compare to others.
(1)[Co(en)(NH3)4]Cl21 chelate ring
(2)[Co(en)3]Cl23 chelate ring
(3)[Co(en)2(NH3)2]Cl22 chelate ring
(4) [Co(NH3)6]Cl20 chelate ring