Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper I covers physical and inorganic chemistry.
Atomic structure: every question, 2021 to 2025
10 parts worth 94 marks have been set on this unit in UPSC IFoS 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.
Quantum theory, 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.
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
- Q2(a)(i) Hydrogen equation in spherical coordinates10 marks Answered
- Q2(a)(ii) Box length from an emission frequency5 marks Answered
- Q2(b)(i) Lifetime and spectral uncertainty5 marks Answered
2024
- Q1(a) Free-particle waves and de Broglie relation8 marks Answered
- Q2(a) Most probable radius in Li²⁺10 marks Answered
2023
- Q1(a) Quantum numbers of oxygen electrons8 marks Answered
- Q2(a) Emission and eigenvalues in a box15 marks Answered
2022
- Q1(a) Continuity of the wavefunction8 marks Answered
- Q2(a) Nodes in hydrogen 3p orbitals10 marks Answered
2021
- Q2(a) Particle in a one-dimensional box15 marks Answered
UPSC Indian Forest Service (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Physical chemistry numericals worked with units; inorganic structures drawn
- Topic-wise weightage and a topic-wise index