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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper I covers inorganic chemistry.

UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper I

Q4(b). Selection rules and absorption intensity

Question

Identify the type of selection rules observed for the following compounds in their electronic absorption spectra. Justify your answer. (i) [Co(NH₃)₆]²⁺ (ii) [NiBr₄]²⁻ (iii) [MnBr₄]²⁻ (iv) [Mn(H₂O)₆]²⁺ (v) KMnO₄

Answer in brief

Spin-allowed d-d bands occur for Co(II) and Ni(II); high-spin Mn(II) d-d bands are spin-forbidden. Permanganate colour arises from intense ligand-to-metal charge transfer.

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Topic notes: electronic spectra of complexes: term symbols, selection rules, Orgel diagrams and charge transfer, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversselection rulesLaporte rulespin selection rulecharge transfer KMnO4d-d transitions

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