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 49 
Pages 3 and 4 of 49 
Pages 5 and 6 of 49 
Pages 7 and 8 of 49 
Pages 9 and 10 of 49
Pages 11 and 12 of 49 Pages 13 and 14 of 49 Pages 15 and 16 of 49 Pages 17 and 18 of 49 Pages 19 and 20 of 49 Pages 21 and 22 of 49 Pages 23 and 24 of 49 Pages 25 and 26 of 49 Pages 27 and 28 of 49 Pages 29 and 30 of 49 Pages 31 and 32 of 49 Pages 33 and 34 of 49 Pages 35 and 36 of 49 Pages 37 and 38 of 49 Pages 39 and 40 of 49 Pages 41 and 42 of 49 Pages 43 and 44 of 49 Pages 45 and 46 of 49 Pages 47 and 48 of 49 Page 49 of 49 
Paper I, physical and inorganic chemistry
Solution, 2025
UPSC Civil Services (Mains), Chemistry optional. 49 pages. All eight questions are answered.
Every question of 2025, one page each44 parts in 8 questions, with the question as text and the key points of its answer
Question 1 50 marks
- 1(a)Probability of the 1s electron at a₀ and at 10a₀5 marks
- 1(b)Born–Haber cycle for NaCl at 298 K5 marks
- 1(c)Raising the conductivity of Ge and Si by trace elements5 marks
- 1(d)Heat conduction between two copper sheets through air5 marks
- 1(e)Superheating of liquids and the Kelvin equation5 marks
- 1(f)Ascending order of dipole moment: NH₃, NF₃, H₂O5 marks
- 1(g)Heat of combustion of naphthalene from bomb calorimetry5 marks
- 1(h)Sealed sample: ethane, neon or a mixture5 marks
- 1(i)Time to plate a gold layer5 marks
- 1(j)Maximum work of a steam turbine5 marks
Question 2 50 marks
Question 3 50 marks
Question 4 50 marks
Question 5 50 marks
- 5(a)Activation energy from two rate constants5 marks
- 5(b)Light absorbed by a dye solution5 marks
- 5(c)Surface area of charcoal from a nitrogen monolayer5 marks
- 5(d)Showing that a decomposition is first order5 marks
- 5(e)Structure of [4Fe–4S] ferredoxin5 marks
- 5(f)Which complex has the larger Δₒ10 marks
- 5(g)Completing five p-block reactions10 marks
- 5(h)Magnetic moment: spin only in the d-block, not in the f-block5 marks
Question 6 50 marks
Question 7 50 marks
- 7(a)T and R forms of haemoglobin15 marks
- 7(b)Cytochrome b, cytochrome c and cytochrome c oxidase5 marks
- 7(c)Stereoisomers of a doubly bridged dicobalt complex10 marks
- 7(d)Second-order rate law with unequal concentrations; units of k10 marks
- 7(e)Substitution in [PtCl₃(C₂H₄)]⁻ and the trans effect10 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.
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.