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Friday, 9 October

JEE Main 2025 · ChemistryMultiple choiceSingle correctMediumMulti-step

JEE Main 3 April 2025, Shift 1, Chemistry Q58

Question 58 of 75 in this shift, Chemistry question 8 of 25, Section A.

In a reaction A+B→C\mathrm{A} + \mathrm{B} \rightarrow \mathrm{C}, initial concentrations of A and B are related as [A]0=8[B]0[\mathrm{A}]_0 = 8[\mathrm{B}]_0. The half lives of A and B are 10 min and 40 min, respectively. If they start to disappear at the same time, both following first order kinetics, after how much time will the concentration of both the reactants be same ?
  1. (1)20 min
  2. (2)40 minOfficial answer
  3. (3)60 min
  4. (4)80 min

Official answer

Option 2

NTA final key.

Chapter
Chemical Kinetics
Topic
Integrated Rate Equations
Idea tested
Concentration After n Half-Lives

Same idea in other shifts

Asked 3× in all
  1. 6 Apr 2026, Shift 1 · Q74Sucrose hydrolyses in acidic medium into glucose and fructose by first order rate law with t1/2=3\mathrm{t_{1/2}}=3 hour. The percentage of…EasyNumerical value
  2. 8 Apr 2025, Shift 2 · Q54In a first order decomposition reaction, the time taken for the decomposition of reactant to one fourth and one eighth of its initial…EasySingle 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. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.