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Friday, 9 October

JEE Main 2025 · ChemistryNumerical answerNumerical valueMediumData or graph

JEE Main 2 April 2025, Shift 2, Chemistry Q71

Question 71 of 75 in this shift, Chemistry question 21 of 25, Section B.

For the reaction A→BA \rightarrow B the following graph was obtained. The time required (in seconds) for the concentration of A to reduce to 2.5 g L−12.5\ \mathrm{g\,L^{-1}} (if the initial concentration of A was 50 g L−150\ \mathrm{g\,L^{-1}}) is __________. (Nearest integer) Given : log⁡2=0.3010\log 2 = 0.3010

The figure, in words

Graph of concentration of A (g/L, y-axis ticks 0, 10, 20, 30, 40, 50) versus time/s (x-axis ticks 5, 10, 15, 20, 25): a decaying curve starting at 50 at t=0, flattening towards about 8; dashed guide lines drop from the curve to the time axis, e.g. 40 near t=5, 30 near t=10, 20 near t=15, and 10 near t=25.

Official answer

43

NTA final key.

Chapter
Chemical Kinetics
Topic
Integrated Rate Equations
Idea tested
First Order Integrated Rate Law

Same idea in other shifts

Asked 5× in all
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  2. 5 Apr 2026, Shift 1 · Q75If the half life of a first order reaction is 6.93 minutes then the time required for completion of 99% of the reaction will be ________…EasyNumerical value
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  4. 16 Mar 2021, Shift 2 · Q58A and B decompose via first order kinetics with half-lives 54.0 min and 18.0 min respectively. Starting from an equimolar non reactive…MediumNumerical value

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 42 of the 174 JEE Main shifts held from 2017 to 2026.