Exams › JEE Main › Chemistry

Correct order of spin only magnetic moment of the following complex ions is (Given At. no. Fe : 26, Co : 27)

1. [Co(C2O4)3]3− > [CoF6]3− > [FeF6]3−
2. [FeF6]3− > [Co(C2O4)3]3− > [CoF6]3−
3. [FeF6]3− > [CoF6]3− > [Co(C2O4)3]3−
4. [CoF6]3− > [FeF6]3− > [Co(C2O4)3]3−

Correct answer: [FeF6]3− > [CoF6]3− > [Co(C2O4)3]3−

Solution

The correct order is based on the number of unpaired electrons in each complex. [FeF6]3− has the highest number of unpaired electrons due to the weak field strength of fluoride ligands, followed by [CoF6]3−, which also has unpaired electrons, while [Co(C2O4)3]3− is a strong field complex that pairs up its electrons, resulting in the lowest magnetic moment.

Related JEE Main Chemistry questions

• When sodium hydroxide is introduced into an aqueous Zn2+ solution, a white precipitate forms, and this precipitate dissolves when more NaOH is added. In such a solution, zinc is present in the:
• When excess ammonia is added to a copper sulphate solution, a deep blue colour appears because of the formation of which species?
• In the nitroprusside ion, iron and NO are present as Fe$^{2+}$ and NO$^+$ instead of Fe$^{3+}$ and NO. These two formulations can be distinguished by
• In the brown ring test for nitrite and nitrate ions, the characteristic brown ring is produced because a complex ion is formed with which formula?
• What is the spin-only magnetic moment, expressed in Bohr magnetons (μB), for Ni²⁺ in aqueous solution? (Atomic number of Ni = 28)
• Silver chloride dissolves in aqueous ammonium hydroxide because it leads to the formation of which species?

⚔️ Practice JEE Main Chemistry free + battle 1v1 →