Concept:A catalyst increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy, without itself being used up.
Explanation:For a reaction to happen, reactant particles must collide with energy equal to or greater than the activation energy.
A catalyst reduces this energy barrier by offering a new, alternative reaction pathway.
Because the activation energy is lower, a greater number of reactant particles can successfully react per unit time.
Thus, the rate of the reaction increases significantly.
The catalyst remains chemically unchanged at the end of the reaction.
It does not lower the overall energy change of the reaction, so option B is incorrect.
Increasing the surface area of reactants, as in option C, is a physical method and is not how a catalyst works.
Proper alignment of molecules, as in option D, applies only to certain biological catalysts, not as a general catalyst mechanism.
Answer:A. providing an alternative reaction pathway