JEE Main 2020ChemistryChemical KineticsEasyMCQ

JEE Main 2020 — Chemical Kinetics Question with Solution

JEE Main 2020 (05 Sep Shift 1)

Question

A flask contains a mixture of compounds A and B. Both compounds decompose by first-order kinetics. The half-lives for A and B are 300 s and 180 s, respectively. If the concentrations of A and B are equal initially, the time required for the concentration of A to be four times that of B (in s) is : (Use ln 2=0.693)

Choose an option

Show full solutionCorrect option: B
Correct answer
B900

Step-by-step explanation

Ct=C0e-kt

kA=ln2300        k=ln2T1/2

kB=ln2180

CtA=C0Ae-kAt        

CtB=C0Be-kBt

Ct,BCt,A=C0,BC0,A×ekA-kBt

14=ekA-kBt

 ln14=ln2300-ln2180t

 -2ln2=ln2300-ln2180t

2=120180×300t

t=2×180×300120=900 sec

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About this question

This is a previous-year question from JEE Main 2020, covering the Chemical Kinetics chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.