Correct option is D
Catalysts, whether homogeneous (same phase as reactants) or heterogeneous (different phase), are substances that increase the rate of a chemical reaction without being consumed in the process. A catalytic promoter enhances the effectiveness of a catalyst, speeding up the reaction. None of these options is responsible for slowing down a reaction. A substance that slows down or inhibits a chemical reaction is called an inhibitor or negative catalyst, which is not listed among the options.
Thus, the correct answer is (d) None of the above.
