JEE Main 2026 · ChemistryMultiple choiceSingle correctMediumMulti-step

JEE Main 5 April 2026, Shift 1, Chemistry Q57

Question 57 of 75 in this shift, Chemistry question 7 of 25, Section A.

First order gas phase reaction

\mathrm{A \rightarrow B + C}

p_i

= initial pressure of gas A,

p_t

= total pressure of the reaction mixture at time

t

Expression of rate constant (

k

) is

(1) $\frac{1}{t}\ln\frac{p_i}{2p_i - p_t}$ Official answer
(2) $\frac{1}{t}\ln\frac{2p_i}{p_i - p_t}$
(3) $\frac{1}{t}\ln\frac{p_i}{3p_i - 2p_t}$
(4) $\frac{1}{t}\ln\frac{3p_i}{4p_i - p_t}$

Official answer

Option 1

NTA final key.

Chapter: Chemical Kinetics
Topic: Integrated Rate Equations
Idea tested: Gas Phase First-Order Kinetics

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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.