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
Question paper, 2025
UPSC Civil Services (Mains), Chemistry optional. 19 pages, as issued by UPSC.
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