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.
All years

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Paper I, physical and inorganic chemistry
Solution, 2017
UPSC Civil Services (Mains), Chemistry optional. 38 pages. All eight questions are answered.
Every question of 2017, one page each35 parts in 8 questions, with the question as text and its full model answer
Question 1 50 marks
- 1(a)Resonance energy; resonance in the carbonate ion10 marks
- 1(b)Most probable speed from the Maxwell distribution10 marks
- 1(c)Joule–Thomson coefficient: definition, unit and -(1)/(C_P)(∂ H/∂ P)_T10 marks
- 1(d)(i)Four phases of sulfur cannot coexist5 marks
- 1(d)(ii)On heating in an open vessel sulfur melts, iodine sublimes5 marks
- 1(e)Debye–Hückel limiting law; γ_± of 0.1 M NaCl10 marks
Question 2 50 marks
Question 3 50 marks
Question 4 50 marks
Question 5 50 marks
- 5(a)Arrhenius equation for zero order; high-temperature limit of k10 marks
- 5(b)Intersystem crossing on the Jablonski diagram10 marks
- 5(c)Signs of Δ G, Δ S and Δ H for adsorption of a gas10 marks
- 5(d)Ferrocene: electrophilic substitution and oxidation10 marks
- 5(e)Why the magnetic moments of Ln³+ ions differ from spin-only values10 marks
Question 6 50 marks
Question 7 50 marks





































