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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2025 · Paper I

Q8(a). Structures of four sulphur nitrides and I₂Cl₆

Question

Draw the structures of S₂N₂, S₄N₂, S₁₁N₂, S₅N₆ and I₂Cl₆.

Answer in brief

S₂N₂: planar four-membered ring; S₄N₂: six-membered ring; S₁₁N₂: two fused eight-membered rings; S₅N₆: basket; I₂Cl₆: planar chlorine-bridged dimer.

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Topic notes: main group chemistry: boranes, borazine, phosphazenes, silicates, silicones, interhalogens, xenon and sulfur–nitrogen compounds, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverssulfur nitridesS2N2S4N4 basketI2Cl6 structureinterhalogen compounds(SN)x polymer

All parts of Question 8