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JEE Advanced 2021 — Paper 1 (Chemistry) Solutions

Step-by-step mathematical proofs, multi-correct partial marking evaluation, and interactive practice for Paper 1.

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Chemistry Questions (17 Questions)

Interactive Partial Marking Mode
Q18Paper 1Chemistry (Inorganic)One or More Correct (Partial Marking)Medium
Coordination Compounds & Qualitative Inorganic Analysis
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q18] Among the following octahedral coordination complexes, which one is diamagnetic (n=0n=0 unpaired electrons) with the highest crystal field stabilization energy (CFSE) magnitude?
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Q19Paper 1Chemistry (Organic)One or More Correct (Partial Marking)Hard
Organic Chemistry & Reaction Mechanisms
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q19] Pinacol (2,3-dimethylbutane-2,3-diol) undergoes acid-catalyzed dehydration to form Pinacolone (3,3-dimethylbutan-2-one). Which of the following statements regarding this transformation is/are CORRECT?
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Q20Paper 1Chemistry (Physical)One or More Correct (Partial Marking)Hard
Chemical Kinetics & Radioactivity
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q20] Consider the consecutive first-order radioactive or chemical decay series A→k1B→k2CA \xrightarrow{k_1} B \xrightarrow{k_2} C, with initial concentration [A]0[A]_0 and [B]0=[C]0=0[B]_0 = [C]_0 = 0. Which of the following statements is/are CORRECT?
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Q21Paper 1Chemistry (Inorganic)One or More Correct (Partial Marking)Hard
Chemical Bonding & Molecular Structure
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q21] According to Molecular Orbital Theory (MOT), which of the following statements regarding O2,O2+,O2−,O_2, O_2^+, O_2^-, and O22−O_2^{2-} is/are CORRECT?
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Q22Paper 1Chemistry (Physical)One or More Correct (Partial Marking)Hard
Electrochemistry & Galvanic Cells
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q22] For the galvanic cell Zn(s)∣Zn2+(aq,0.01 M) ∣∣ Cu2+(aq,1.0 M)∣Cu(s)Zn(s) | Zn^{2+}(aq, 0.01\text{ M}) \,||\, Cu^{2+}(aq, 1.0\text{ M}) | Cu(s) at 298 K298\text{ K}, given standard reduction potentials EZn2+/Zn∘=−0.76 VE^\circ_{Zn^{2+}/Zn} = -0.76\text{ V} and ECu2+/Cu∘=+0.34 VE^\circ_{Cu^{2+}/Cu} = +0.34\text{ V}. Which of the following statements is/are CORRECT? (Take 2.303RTF=0.059 V\frac{2.303 RT}{F} = 0.059\text{ V}).
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Q23Paper 1Chemistry (Inorganic)One or More Correct (Partial Marking)Medium
p-Block Elements (Groups 13 to 18)
Scoring Scheme: +4 Full Marks • -2 Negative Marks • Partial Marking Enabled
[JEE Advanced 2021 Paper 1 Chemistry Q23] Which of the following statements regarding Diborane (B2H6B_2H_6) and Oxyacids of Phosphorus is/are CORRECT?
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Q24Paper 1Chemistry (Physical)Numerical Value TypeMedium
Solid State & Crystal Lattices
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q24] An element crystallizes in a Face-Centered Cubic (FCC) unit cell with edge length a=410 pma = 410\text{ pm}. If the molar mass of the element is M=70 g/molM = 70\text{ g/mol} and Avogadro's number NA=6.022×1023 mol−1N_A = 6.022 \times 10^{23}\text{ mol}^{-1}, calculate the density of the crystal in g/cm3\text{g/cm}^3.
Q25Paper 1Chemistry (Physical)Numerical Value TypeMedium
Ionic & Chemical Equilibrium
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q25] An acidic buffer is prepared by mixing sodium acetate (CH3COONaCH_3COONa) and acetic acid (CH3COOHCH_3COOH, pKa=4.76pK_a = 4.76) in the molar ratio [Salt][Acid]=1.50\frac{[\text{Salt}]}{[\text{Acid}]} = 1.50. Calculate the resulting pH of the buffer solution at 25∘C25^\circ\text{C}.
Q26Paper 1Chemistry (Physical)Numerical Value TypeMedium
Solutions & Colligative Properties
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q26] What is the depression in freezing point ΔTf\Delta T_f (in K) of a solution prepared by dissolving 18.0 g18.0\text{ g} of glucose (C6H12O6C_6H_{12}O_6, molar mass =180 g/mol= 180\text{ g/mol}) in 1000 g1000\text{ g} of pure water? (Cryoscopic constant of water Kf=1.86 K kg/molK_f = 1.86\text{ K kg/mol}).
Q27Paper 1Chemistry (Physical)Numerical Value TypeMedium
Electrochemistry & Electrolysis
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q27] An aqueous solution of CuSO4CuSO_4 is electrolyzed with a steady electric current of I=9.65 AI = 9.65\text{ A} for t=1000 secondst = 1000\text{ seconds}. How many moles of electrons are transferred through the cell? (Faraday constant F=96500 C/molF = 96500\text{ C/mol}).
Q28Paper 1Chemistry (Physical)Numerical Value TypeMedium
Chemical Kinetics
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q28] The rate of a chemical reaction doubles when the temperature is raised from 300 K300\text{ K} to 310 K310\text{ K}. Given R=8.314 J/(mol K)R = 8.314\text{ J/(mol K)} and ln⁡2≈0.693\ln 2 \approx 0.693, determine the activation energy EaE_a (in kJ/mol). (Round off to one decimal place).
Q29Paper 1Chemistry (Inorganic)Numerical Value TypeMedium
Coordination Compounds
Scoring Scheme: +4 Full Marks • 0 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q29] Calculate the spin-only magnetic moment μs\mu_s (in Bohr Magnetons, BM) for the high-spin complex [Fe(H2O)6]2+[Fe(H_2O)_6]^{2+}. (Given: 24≈4.90\sqrt{24} \approx 4.90).
Q30Paper 1Chemistry (Organic)Single Correct OptionMedium
Haloalkanes & Haloarenes
Scoring Scheme: +3 Full Marks • -1 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q30] Reaction of (R)(R)-2-bromobutane with sodium hydroxide (NaOHNaOH) in acetone follows a bimolecular nucleophilic substitution (SN2S_N2) mechanism. The configuration of the major alcohol product formed is:
Q31Paper 1Chemistry (Organic)Single Correct OptionMedium
Aldehydes, Ketones and Carboxylic Acids
Scoring Scheme: +3 Full Marks • -1 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q31] When acetaldehyde (CH3CHOCH_3CHO) is warmed with dilute aqueous NaOHNaOH followed by heating with acid, the final major product formed is:
Q32Paper 1Chemistry (Organic)Single Correct OptionMedium
Aromatic Hydrocarbons
Scoring Scheme: +3 Full Marks • -1 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q32] Treatment of benzene with 1-chloropropane in the presence of anhydrous aluminium chloride (AlCl3AlCl_3) yields isopropylbenzene (Cumene) as the major product rather than n-propylbenzene because:
Q33Paper 1Chemistry (Inorganic)Single Correct OptionHard
Qualitative Inorganic Salt Analysis
Scoring Scheme: +3 Full Marks • -1 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q33] In the brown ring test for nitrate ion (NO3−NO_3^-), the brown ring formed at the junction of the two liquid layers is due to the formation of the complex:
Q34Paper 1Chemistry (Organic)Single Correct OptionMedium
Biomolecules & Carbohydrates
Scoring Scheme: +3 Full Marks • -1 Negative Marks
[JEE Advanced 2021 Paper 1 Chemistry Q34] α\alpha-D-glucopyranose and β\beta-D-glucopyranose are related to each other as: