Which statement best describes a catalyst?

A catalyst is defined primarily by its ability to lower the activation energy barrier of a chemical reaction, thereby increasing the reaction rate. This reduction in activation energy allows more reactant molecules to possess sufficient energy to react, accelerating the formation of products without the catalyst itself undergoing any permanent change in the process.

This characteristic is fundamental as it distinguishes catalysts from other substances that may affect reaction rates. While a catalyst increases the speed of a reaction, it does not alter the overall energy change of the reaction or the position of equilibrium in a reversible reaction. Option B effectively encapsulates this core function of a catalyst, making it the most accurate description among the provided choices.

Other options present aspects that do not accurately reflect the role of a catalyst. For instance, the first option mentions an increase in reaction time, which misrepresents the function of a catalyst. The third option suggests that a catalyst can change the equilibrium position, which is incorrect since a catalyst speeds up both the forward and reverse reactions equally, thereby leaving the equilibrium point unchanged. The last option states that a catalyst is not necessary for a chemical reaction, while it is true that reactions can occur without catalysts, their primary role is to enhance the rate of reactions that would otherwise proceed very slowly. Thus