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.
Solid state: every question, 2021 to 2025
12 parts worth 125 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.
Crystal systems; designation of crystal faces, lattice structures and unit cell; Bragg's law; X-ray diffraction by crystals; close packing, radius ratio rules, calculation of some limiting radius ratio values; structures of NaCl, ZnS, CsCl and CaF₂; stoichiometric and nonstoichiometric defects, impurity defects, semi-conductors.
Notes: Defects in solids, non-stoichiometry and semiconductors (full notes) · short notes
Notes: Crystal systems, Miller indices, Bragg's law and radius ratio (full notes) · short notes
2025
- Q1(c) Raising the conductivity of Ge and Si by trace elements5 marks Answered
- Q2(c) Radius ratio and the structure of ZnS15 marks Answered
- Q2(d) Stoichiometry of NaCl doped with Ca²⁺5 marks Answered
- Q3(e) Why crystals have more defects at higher temperature5 marks Answered
2024
- Q1(b)(ii) Unit cell and the cubic Bravais lattices5 marks Answered
- Q2(c)(i) Limiting radius ratio for coordination numbers 3 and 610 marks Answered
- Q2(c)(ii) Stoichiometric defects10 marks Answered
2023
- Q1(c) Bragg equation and the layer spacing10 marks Answered
- Q2(c) Primitive cubic lattice: points, voids and the sphere at the centre10 marks Answered
2022
2021
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