A catalyst:

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction mechanism with a lower activation energy ($E_a$). \nKey characteristics of a catalyst include: 1. **Kinetic Effect**: It lowers the energy barrier ($E_a$) for both the forward and reverse reactions, allowing the system to reach equilibrium faster. 2. **Conservation**: Although it may participate in intermediate steps, it is regenerated by the end of the reaction and is not consumed. 3. **Thermodynamic Neutrality**: It does not change the enthalpy ($\Delta H$), the Gibbs free energy ($\Delta G$), or the equilibrium constant ($K_{eq}$) of the reaction. It only affects the kinetics (speed). 4. **Product Identity**: The identity and amount of products at equilibrium remain unchanged. \nTherefore, the correct choice is that a catalyst lowers $E_a$ without being consumed.