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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2025 · Paper I

Q2(b)(ii). Dissociation energies of dioxygen species

Question

Energies needed to dissociate one O atom from dioxygen species are 642, 494, 394 and 210 kJ/mol. Correlate these with O₂²⁻, O₂⁻, O₂ and O₂⁺ using MO theory.

Answer in brief

Assign 642 to O₂⁺, 494 to O₂, 394 to O₂⁻ and 210 kJ/mol to O₂²⁻; their formal bond orders are 2.5, 2, 1.5 and 1, respectively.

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Topic notes: molecular orbital theory: LCAO, MO diagrams of N₂, O₂, CO, NO, CN⁻ and HF, bond order and magnetism, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversMO theory of O₂bond ordersuperoxide and peroxidedissociation energyπ* antibonding orbitals

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