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.
Main group chemistry: every question, 2021 to 2025
14 parts worth 140 marks have been set on this unit in UPSC CSE Chemistry Paper I from 2021 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Boranes, borazines, phosphazenes and cyclic phosphazene, silicates and silicones, interhalogen compounds; sulphur–nitrogen compounds, noble gas compounds.
Notes: VSEPR, hybridisation and Bent's rule (full notes) · short notes
Notes: Non-aqueous solvents: liquid NH₃, HF, H₂SO₄, SO₂, BrF₃ and superacids (full notes) · short notes
Notes: Main group chemistry: boranes, borazine, phosphazenes, silicates, silicones, interhalogens, xenon and S–N compounds (full notes) · short notes
2025
- Q5(g) Completing five p-block reactions10 marks Answered
- Q8(a) Structures of four sulphur nitrides and I₂Cl₆10 marks Answered
- Q8(b) Silicones, hexamethyldisiloxane and chain stopping10 marks Answered
2024
- Q8(a) Why all F atoms of PF₅ look alike in the ¹⁹F NMR spectrum10 marks Answered
- Q8(b)(i) Possible arrangements and shape of ClF₃10 marks Answered
- Q8(b)(ii) Structure and bonding of B₂H₆10 marks Answered
2023
- Q4(d) Pyroxenes, amphiboles and phyllosilicates10 marks Answered
- Q6(a) Completing five reactions of p-block compounds10 marks Answered
- Q6(e) Framework electrons and structures of three borane anions10 marks Answered
2022
- Q5(e) Lower cyclosiloxanes: synthesis and structure of (Me₂SiO)₃10 marks Answered
- Q6(d) Separating XeF₆; diborane with NH₃ and with Me₃N10 marks Answered
2021
- Q5(e) Completing five reactions of xenon compounds10 marks Answered
- Q6(a) Bonding in cyclic phosphazene, benzene and borazine10 marks Answered
- Q8(a) BrF₃ as an aprotic solvent: acids, bases and neutralisation10 marks Answered
UPSC Civil Services (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Question choice and time plan for each paper
- Topic-wise weightage and a topic-wise index