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Saturday, 31 October

JEE Main 2025 · ChemistryNumerical answerNumerical valueMediumMulti-step

JEE Main 2 April 2025, Shift 2, Chemistry Q75

Question 75 of 75 in this shift, Chemistry question 25 of 25, Section B.

Consider the above sequence of reactions. 151 g of 2-bromopentane is made to react. Yield of major product P is 80% whereas Q is 100%. Mass of product Q obtained is __________ g. (Given molar mass in g mol−1\mathrm{g\ mol^{-1}} H : 1, C : 12, O : 16, Br : 80)

The figure, in words

Reaction scheme: 2-bromopentane (skeletal zig-zag chain with Br on carbon 2) reacts with alcoholic KOH to give P (major product), which then reacts with Br2 to give Q.

Official answer

184

NTA final key.

Chapter
Haloalkanes and Haloarenes
Topic
Alkenes and Alkynes
Idea tested
Saytzeff vs. Hofmann Elimination

Same idea in other shifts

Asked 7× in all
  1. 5 Apr 2024, Shift 2 · Q77Identify the major product in the following reaction. 1-bromo-1-methylcyclopentane…EasyDiagram basedHas a figure
  2. 25 Jun 2022, Shift 1 · Q75The major product in the reaction [figure: CH3−C(CH3)(CH3)−Cl\mathrm{CH_3-C(CH_3)(CH_3)-Cl} (central C with CH3\mathrm{CH_3} above, CH3\mathrm{CH_3} below,…EasySingle correctHas a figure
  3. 31 Aug 2021, Shift 2 · Q41The major product of the following reaction is : [reaction: starting material drawn as a five-membered ring; reagent above/below arrow:…MediumDiagram basedHas a figure
  4. 2 Sep 2020, Shift 2 · Q44The major product obtained from E2\mathrm{E_2}-elimination of 3-bromo-2-fluoropentane is :HardSingle correctHas a figure
  5. 2 Apr 2017 (offline) · Q52Which of the following, upon treatment with *tert*-BuONa followed by addition of bromine water, fails to decolourize the colour of bromine ?HardSingle correctHas a figure
  6. 2 Apr 2017 (offline) · Q56The major product obtained in the following reaction is : [reaction: (+)-C6H5CH(Br)CH2C6H5\mathrm{C_6H_5CH(Br)CH_2C_6H_5} (Br on wedge, H on hash at the…MediumSingle correctHas a figure

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.