Understanding the Concept:
A catalyst changes the rate of a reaction by providing an alternative reaction pathway having lower activation energy.
Step 1: Understanding activation energy.
Activation energy is the minimum energy required for reactant molecules to undergo effective collision and convert into products.
Without catalyst:
\[
E_a=\text{high}
\]
With catalyst:
\[
E_a=\text{lower}
\]
Thus, more molecules acquire sufficient energy to react, increasing the reaction rate.
Step 2: Checking thermodynamic quantities.
A catalyst affects only the kinetics of a reaction, not the thermodynamic properties.
Therefore:
\[
\Delta H,\ \Delta G,\ \Delta S
\]
remain unchanged.
Similarly, internal energy also remains unchanged.
Step 3: Conclusion.
Only activation energy is altered by a catalyst.
Hence, option (2) is correct.