Read the passage carefully and answer the questions.

The speed at which a chemical reaction takes place is called the rate of reaction. The rate of reaction depends on various factors like concentration of the reactants, temperature, etc. The relation between the rate of reaction and the concentration of reacting species is represented by the equation $r = k[A]^x[B]^y$, where $x$ and $y$ are the order of the reaction with respect to the reactants A and B, respectively. The overall order of the reaction is $x + y$. The rate of reaction can also be increased by the use of a catalyst which provides an alternate pathway of lower activation energy. It increases the rate of forward and backward reaction to an equal extent. It does not alter the Gibbs energy of the reaction.

The role of a catalyst is to change

Activation energy of a reaction.

The correct answer is Option (3) → Activation energy of a reaction.

• A catalyst provides an alternate reaction pathway with lower activation energy, which increases the rate of both forward and backward reactions.
• It does not change the Gibbs energy (ΔG), enthalpy (ΔH), or the equilibrium constant (K) of the reaction.

 Hence, the correct option is Activation energy of a reaction.