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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

Q3(b)(i). Composition after hydrogen leakage

Question

A balloon contains H₂ and O₂, both leaking through pores. If 45% of H₂ leaks, what is the O₂/H₂ ratio left?

Answer in brief

A unique ratio needs the initial composition and a leakage model; for an initially equimolar mixture, the constant-rate approximation gives 1.614 and integrated molecular effusion gives 1.566.

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: kinetic theory of gases, Maxwell distribution and effusion, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversGraham's law of effusioneffusion of H₂ and O₂rate of effusionmolar mass dependence

All parts of Question 3