Activation energy is:

Engineering

Chemistry

Arrhenius Equation

Catalysis and Kinetics

Order of Reaction and Law of Mass Action

Question

Activation energy is:

the energy which a molecule should have in order to enter into an effective collision.

the amount of energy to be added to the actual energy of a molecule so that the threshold energy is reached.

the amount of energy the molecule must contain so that it reacts.

the average kinetic energy of the molecule.

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Explanation:
The energy difference between the energy of reactant E_r and threshold energy E_t is activation energy as shown below figure:

Therefore, option A is the correct answer.