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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2025 · Paper I

Q4(a)(i). Boiling point at reduced atmospheric pressure

Question

For water, ΔHvap = 40.65 kJ/mol and the normal boiling point is 373.15 K. Find the boiling point on a mountain of height 5500 m where pressure is 380 torr.

Model answer

The free solution for 2025 answers questions 1, 2, 3, 5 and 6, the ones picked in its time plan. Question 4 is answered in full in the IFoS Chemistry Paper I, 2021 to 2025 book, with every part of every paper.

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Cover of UPSC Indian Forest Service (Main) Chemistry Paper I: Model Answers 2021 to 2025
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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
Printed copyKindle editionRead sample pages

Topic notes: the phase rule, phase diagrams, the Clausius–Clapeyron equation, eutectics and partially miscible liquids, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversClausius–Clapeyron equationboiling point at high altitudeenthalpy of vaporisationvapour pressure

All parts of Question 4