1. [Co(NH₃)₆]₂(SO₄)₃ 2. [Co(NH₃)₄(H₂O)Br](NO₃)₂ 3. [Co(NH₃)₃(NO₃)₃] 4. [CoCl₂(en)₂]NO₃

Topic: Werner's theory, ligands, coordination number, denticity, chelation· Coordination Compounds

Which complex compound is most stable?

1. \([\mathrm{Co(NH_3)_6}]_2(\mathrm{SO_4})_3\)

2. \([\mathrm{Co(NH_3)_4(H_2O)Br}](\mathrm{NO_3})_2\)

3. \([\mathrm{Co(NH_3)_3(NO_3)_3}]\)

4. \([\mathrm{CoCl_2(en)_2}]\mathrm{NO_3}\)

Doubtly Asked 30 Oct 2026 NEET UG 2023 Practice test neet Save WhatsApp Report

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Answer: 4. \([\mathrm{CoCl_2(en)_2}]\mathrm{NO_3}\)

Key idea: A chelating ligand makes a complex more stable (chelate effect).

In \(\mathrm{[CoCl_2(en)_2]NO_3}\), the ligand en (ethane-1,2-diamine) is bidentate and forms two five-membered chelate rings. The other complexes have only monodentate ligands. So option 4 is the most stable.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Which complex compound is most stable?

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