Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper I covers physical and inorganic chemistry.
All topics
Paper I, physical and inorganic chemistry
Photochemistry: every question, 2021 to 2025
8 parts worth 81 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.
Syllabus
Absorption of light; decay of excited state by different routes; photochemical reactions between hydrogen and halogens and their quantum yields.
Notes: Photochemistry: quantum yield, Jablonski diagram, H₂–halogen reactions (full notes) · short notes
2025
- Q6(a)(ii) Fluorescence and phosphorescence5 marks Answered
- Q6(c) Photochemical hydrogen–bromine reaction10 marks Answered
2024
- Q1(c) Primary quantum yield8 marks Answered
- Q3(c) Photostationary dimer concentration10 marks Question only
2023
- Q6(b) Threshold wavelength for excitation15 marks Answered
2022
- Q6(a) Singlet and triplet excited states10 marks Answered
2021
- Q5(b) Stark–Einstein law8 marks Answered
- Q6(b) Quantum yield and ethylene production15 marks Answered
Printed copy and Kindle
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