Learn

Saturday, 31 October

JEE Main 2021 · ChemistryMultiple choiceSingle correctEasyApplication

JEE Main 26 August 2021, Shift 1, Chemistry Q42

Question 42 of 90 in this shift, Chemistry question 12 of 30, Section A.

Excess of isobutane on reaction with Br2\mathrm{Br_2} in presence of light at 125℃ gives which one of the following, as the major product ?

The figure, in words

Options are drawn condensed structural formulas (labels as printed); the vertical substituent is joined to the central C/CH by a single vertical line.
  1. (1)[structure] CH3−CH−CH2Br\mathrm{CH_3-CH-CH_2Br} with CH3\mathrm{CH_3} below the CH (drawn vertically)
  2. (2)[structure] CH3−C−Br\mathrm{CH_3-C-Br} with CH3\mathrm{CH_3} above and CH3\mathrm{CH_3} below the COfficial answer
  3. (3)[structure] CH3−C−CH2−Br\mathrm{CH_3-C-CH_2-Br} with Br above and CH3\mathrm{CH_3} below the C
  4. (4)[structure] CH3−CH−CH2Br\mathrm{CH_3-CH-CH_2Br} with CH2Br\mathrm{CH_2Br} below the CH (drawn vertically)

Official answer

Option 2

NTA final key.

Chapter
Hydrocarbons
Topic
Alkanes and Free Radicals
Idea tested
Reactivity-Selectivity Principle

Same topic in other shifts

All Alkanes and Free Radicals questions
  1. 2 Apr 2026, Shift 1 · Q73One mole of an alkane (x) requires 88 mole oxygen for complete combustion. Sum of number of carbon and hydrogen atoms in the alkane (x)…EasyNumerical value
  2. 2 Apr 2026, Shift 2 · Q64The compound (X) on heating in the presence of anhydrous AlCl3_3 and HCl gas gives 2,4-dimethyl pentane (ii) aromatization gives toluene…EasySingle correct
  3. 5 Apr 2026, Shift 2 · Q72RMgI when treated with ice cold water liberated a gas which occupied 1.4 dm3^3/g at STP. The gas produced is further reacted with iodine…MediumNumerical value
  4. 6 Apr 2026, Shift 1 · Q65Given below are two statements: Statement I: Methane can be prepared by decarboxylation of sodium ethanoate, Kolbe's electrolysis of…MediumTwo statements
  5. 6 Apr 2026, Shift 2 · Q72An alkane (Y) requires 8 moles of oxygen for complete combustion and on chlorination with Cl2/hν\mathrm{Cl_2}/h\nu, (Y) gives only one…MediumNumerical value
  6. 8 Apr 2026, Shift 2 · Q65n-Butane on monochlorination under photochemical condition gives an optically active compound "P". "P" on further chlorination gives…MediumSingle correct

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.