Rate of a reaction can be expressed by Arrhenius equation as: k = A\,e^ - E/RT In this equation, E represents

the energy above which all the colliding molecules will react

the energy below which colliding molecules will not react

the total energy of the reacting molecules at a temperature, T

the fraction of molecules with energy greater than the activation energy of the reaction

Chemical Kinetics and Nuclear Chemistry PYQ — JEE Main 2006 · Shift 0 · Q28 with Solution

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Correct answer: A

$k = A e^{-E/RT}$

where:

Activation energy is the minimum energy barrier that reacting molecules must possess for effective collision and reaction to occur.

Option A: "the energy above which all the colliding molecules will react"
- This best matches the JEE-level interpretation of activation energy: molecules having energy equal to or greater than activation energy are capable of reaction.
- Hence, this is the correct option.
Option B: "the energy below which colliding molecules will not react"
- This is also close in wording to activation energy, but it describes the threshold indirectly rather than defining $E$ itself in the usual exam sense.
- In standard MCQ conventions, option A is preferred.
Option C: "the total energy of the reacting molecules at a temperature, $T$ "
- Incorrect. $E$ is not the total energy of molecules.
Option D: "the fraction of molecules with energy greater than the activation energy of the reaction"
- Incorrect. That fraction is related to the exponential factor $e^{-E/RT}$ , not $E$ itself.

$\boxed{A}$