UPSC Chemistry 2025

(a) Calculate the ratio of probability of finding the 1s electron of hydrogen atom at r = a₀ and at r = 10a₀, where 'r' is the distance from the nucleus and a₀ = radius of the fir…

(a) Find the probability of existence of a particle in a one-dimensional box of length 'a' in the region 0 ≤ x ≤ a/4 for the states n = 1, 2 and 3. (15 marks) (b) The standard red…

(a) Calculate the number of collisions that oxygen makes per second on 1·00 cm² of the surface of the vessel containing them if the pressure is 1·00 × 10⁻⁶ atm and the temperature…

(a) Draw the molecular orbital (MO) diagram of NO molecule. The experimental bond dissociation energy of NO is 626 kJ mol⁻¹ while that of NO⁺ is 1047 kJ mol⁻¹ — rationalize it. NO…

(a) The gas-phase reaction between methane (CH₄) and diatomic sulphur (S₂) is given by the following reaction: CH₄ (g) + 2S₂ (g) ———→ CS₂ (g) + 2H₂S (g). At 823 K, the rate consta…

(a) The following molecule shows the rigid or fluxional behaviour at higher temperature or in the presence of a base. Justify the answer with the help of ¹H NMR spectrum. (10 mark…

(a) Distinguish the "T" (tense) and 'R' (relax) conformations of Hemoglobin on reversible binding of oxygen (O₂). 15 marks (b) What is the basic difference between Cytochrome 'b'…

(a) Draw the structures of S₂N₂, S₄N₂, S₁₁N₂, S₅N₆ and I₂Cl₆. 10 marks (b) What are silicones ? Mention some of their uses. How will you prepare hexamethyldisiloxane ? Draw its st…

(a) (i) Tropolone is aromatic, but fulvene is non-aromatic. Why? (ii) Explain with example pseudo-aromaticity. (b) Identify the missing reagent and intermediates in the following…

(a) (i) In the presence of sodium ethoxide, the following transformation occurs. Explain : (ii) Propose a suitable mechanism for the following transformation : (b) (i) The followi…

(a) (i) Write the structure of the product formed in the following reactions: (1) (2) (10 marks) (ii) Describe the synthesis of ketone (A) when only isobutanol is available as the…

(a) (i) After polymerization of p-hydroxybenzoic acid, IR analysis shows 0·2% unreacted —COOH. Calculate the molecular weight of the polymer and categorize it. (7 marks) (ii) Writ…

(a) Write the structure of the product(s) and the intermediate formed in the following reaction: Cl₂CH—COCl 1) Et₃N → ? 2) Cyclopentadiene, Heat (10 marks) (b) Deduce the structur…

(a) (i) Elucidate the structure of the product and the intermediate (if any) in the following reactions: (A) [structure: H(Me)C(CO₂Et)(CH₂CO₂H)] 1) BH₃ 2) H⁺ → ? (B) [structure: c…

(a) (i) Acetone shows a weak absorption at 280 nm and a strong absorption at 190 nm in the UV spectrum. Account for the observation. (5 marks) (ii) Using Woodward-Fieser rules, ca…

(a) (i) Estimate the expected splitting (coupling constant J in Hz) for the lettered protons in the ¹H NMR spectrum of the following compounds: (1) A, (2) B, (3) C (5 marks) (ii)…