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.
Atomic structure: every question, 2021 to 2025
10 parts worth 105 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.
Heisenberg's uncertainty principle, Schrodinger wave equation (time independent); interpretation of wave function, particle in one-dimensional box, quantum numbers, hydrogen atom wave functions; shapes of s, p and d orbitals.
Explained on the blog: Particle in a box: probability in part of the box (asked in 2022 and 2025)
Notes: Particle in a one-dimensional box (full notes) · short notes
Notes: Postulates of quantum mechanics: operators, eigenfunctions, Hermitian operators and acceptable wave functions (full notes) · short notes
Notes: Uncertainty principle, de Broglie relation and wave–particle duality (full notes) · short notes
Notes: Hydrogen atom: Schrödinger equation, quantum numbers, radial distribution, nodes and orbital shapes (full notes) · short notes
2025
- Q1(a) Probability of the 1s electron at a₀ and at 10a₀5 marks Answered
- Q2(a) Particle in a box: probability in the first quarter15 marks Answered
2024
- Q1(a)(i) Most probable distance of the 1s electron5 marks Answered
- Q2(a) Uncertainty principle; orthogonality of ψ₁ and ψ₂ in a box10 marks Answered
2023
2022
- Q1(a) Average and most probable distance of the 1s electron10 marks Answered
- Q2(b) Particle in a box: probability in the first 1/a of the width20 marks Answered
2021
- Q1(a) Expectation value of position in the ground state of a box10 marks Answered
- Q2(a) Hydrogen atom: the transition n = 101 → 10010 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