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 50 
Pages 3 and 4 of 50 
Pages 5 and 6 of 50 
Pages 7 and 8 of 50
Pages 9 and 10 of 50 Pages 11 and 12 of 50 Pages 13 and 14 of 50 Pages 15 and 16 of 50 Pages 17 and 18 of 50 Pages 19 and 20 of 50 Pages 21 and 22 of 50 Pages 23 and 24 of 50 Pages 25 and 26 of 50 Pages 27 and 28 of 50 Pages 29 and 30 of 50 Pages 31 and 32 of 50 Pages 33 and 34 of 50 Pages 35 and 36 of 50 Pages 37 and 38 of 50 Pages 39 and 40 of 50 Pages 41 and 42 of 50 Pages 43 and 44 of 50 Pages 45 and 46 of 50 Pages 47 and 48 of 50 Pages 49 and 50 of 50 
Paper I, physical and inorganic chemistry
Solution, 2024
UPSC Civil Services (Mains), Chemistry optional. 50 pages. All eight questions are answered.
Every question of 2024, one page each47 parts in 8 questions, with the question as text and the key points of its answer
Question 1 50 marks
- 1(a)(i)Most probable distance of the 1s electron5 marks
- 1(a)(ii)Lattice energies of NaBr and NaI above the calculated values5 marks
- 1(b)(i)Separation factor for ²³⁵UF₆ and ²³⁸UF₆ in one effusion stage5 marks
- 1(b)(ii)Unit cell and the cubic Bravais lattices5 marks
- 1(c)Normal boiling point of mercury10 marks
- 1(d)(i)Will CCl₂F₂ condense at 18 atm and 20 °C?5 marks
- 1(d)(ii)Overvoltage and its applications5 marks
- 1(e)Temperature at which the uncatalysed reaction matches catalase at 20 °C10 marks
Question 2 50 marks
Question 3 50 marks
- 3(a)(i)Viscosity of air at 298 K and at 0 K10 marks
- 3(a)(ii)Boyle temperature of Ar, CH₄ and C₆H₆5 marks
- 3(b)(i)Surface tension: ethanol or dimethyl ether5 marks
- 3(b)(ii)Pressure difference across a water droplet of radius 150 nm5 marks
- 3(c)(i)Change in Helmholtz energy on reversible isothermal compression10 marks
- 3(c)(ii)Why a tyre gets hot when it is pumped5 marks
- 3(c)(iii)Pressure of O₂ over NiO at 25 °C5 marks
- 3(c)(iv)Final temperature after Joule–Thomson expansion5 marks
Question 4 50 marks
- 4(a)Triple point, stable phase and enthalpy of sublimation of a new drug15 marks
- 4(b)(i)Polarography and concentration polarisation15 marks
- 4(b)(ii)Concentration cells; fuel cells as energy converters5 marks
- 4(c)(i)Time of maximum concentration of B in A → B → C10 marks
- 4(c)(ii)Yield of P₁ from three parallel paths5 marks
Question 5 50 marks
- 5(a)Fluorescence and phosphorescence on a Jablonski diagram10 marks
- 5(b)(i)How water condenses onto glass5 marks
- 5(b)(ii)Time to form half a monolayer at 2.0 × 10⁻¹¹ torr5 marks
- 5(c)IUPAC names of five complexes10 marks
- 5(d)Zeise's salt: synthesis and structure10 marks
- 5(e)(i)Lanthanide contraction5 marks
- 5(e)(ii)Why Hf is placed below Zr5 marks
Question 6 50 marks
Question 7 50 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.
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.
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.
Model answer pages open with the VKC plan.
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.