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
Pages 1 and 2 of 54 
Pages 3 and 4 of 54 
Pages 5 and 6 of 54 
Pages 7 and 8 of 54
Pages 9 and 10 of 54 Pages 11 and 12 of 54 Pages 13 and 14 of 54 Pages 15 and 16 of 54 Pages 17 and 18 of 54 Pages 19 and 20 of 54 Pages 21 and 22 of 54 Pages 23 and 24 of 54 Pages 25 and 26 of 54 Pages 27 and 28 of 54 Pages 29 and 30 of 54 Pages 31 and 32 of 54 Pages 33 and 34 of 54 Pages 35 and 36 of 54 Pages 37 and 38 of 54 Pages 39 and 40 of 54 Pages 41 and 42 of 54 Pages 43 and 44 of 54 Pages 45 and 46 of 54 Pages 47 and 48 of 54 Pages 49 and 50 of 54 Pages 51 and 52 of 54 Pages 53 and 54 of 54 
Paper I, physical and inorganic chemistry
Solution, 2022
UPSC Civil Services (Mains), Chemistry optional. 54 pages. All eight questions are answered.
Every question of 2022, one page each38 parts in 8 questions, with the question as text and the key points of its answer
Question 1 50 marks
- 1(a)Average and most probable distance of the 1s electron10 marks
- 1(b)Non-bonding interactions between orbitals of A and B10 marks
- 1(c)F-centres: one colour by every route; effect on density10 marks
- 1(d)ΔG for the formation of ozone in smog10 marks
- 1(e)ΔG° and K for the zinc–copper cell reaction10 marks
Question 2 50 marks
Question 3 50 marks
- 3(a)The least stable of OCN⁻, ONC⁻ and SCN⁻10 marks
- 3(b)Entropy changes when an ice cube melts in the sea at 0 °C10 marks
- 3(c)Speed distribution curves of argon and helium10 marks
- 3(d)Phase diagram of water; critical point and triple point10 marks
- 3(e)Forces on an ion moving through a strong-electrolyte solution10 marks
Question 4 50 marks
- 4(a)The state of H₂ corresponding to N₂ at 126 K and 1 atm10 marks
- 4(b)Mean molar heat of vaporisation of water from two vapour pressures10 marks
- 4(c)Capillary rise of two liquids in the same tube10 marks
- 4(d)Principle of polarography; reading a polarogram10 marks
- 4(e)Percentage ionic character of the Br–Cl bond10 marks
Question 5 50 marks
- 5(a)Product concentration in a first-order reaction, N₂O₂ → 2NO10 marks
- 5(b)Jablonski diagram (A to E); the route to photochemistry10 marks
- 5(c)Allosteric effect and homotropic modulators10 marks
- 5(d)[Ni(CO)₄] and [Ni(CN)₄]⁴⁻: names, structures and shapes10 marks
- 5(e)Lower cyclosiloxanes: synthesis and structure of (Me₂SiO)₃10 marks
Question 6 50 marks
- 6(a)Metal–metal bonds in Cp₂Fe₂(CO)₄; structure of Bi₅³⁺10 marks
- 6(b)Pale colours and line-like spectra of lanthanide ions10 marks
- 6(c)Neutral mixed sandwich compound of a d⁶ centre10 marks
- 6(d)Separating XeF₆; diborane with NH₃ and with Me₃N10 marks
- 6(e)Origin of the yellow colour of aqueous FeCl₃10 marks
Question 7 50 marks
- 7(a)An optically active square-planar complex10 marks
- 7(b)Aqueous LaCl₃ and LuCl₃: which is more acidic10 marks
- 7(c)Opposing first-order reactions: time to form half the equilibrium amount10 marks
- 7(d)Surface area of an adsorbent from the nitrogen monolayer10 marks
- 7(e)Magnetic behaviour of copper(II) acetate and [Cu(CN)₄]³⁻10 marks
Question 8 50 marks
- 8(a)The more stable linkage isomer of a cyanide-bridged complex10 marks
- 8(b)Haemocyanin: active site, colours and functions10 marks
- 8(c)Stationary and branching chain reactions; conditions for explosion10 marks
- 8(d)Steady-state approximation; photochemical H₂ + Cl₂; quantum yield10 marks
- 8(e)Langmuir isotherm and the kinetics of surface reactions10 marks
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Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
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Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
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Model answer pages open with the VKC plan.
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Printed copy and Kindle
UPSC Civil Services (Main) Chemistry Paper I: Model Answers 2021 to 2025
The book has all five years of Paper I in one volume, with every question printed above its answer, a time plan for each paper, the topic-wise weightage of marks and a topic-wise index.