Chemistry
Answer
(a) Chemical reaction — Any chemical change in matter which involves transformation into one or more substances with entirely different properties is called a chemical reaction.
(b) Catalyst — A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.
(c) Promoter — Substances that improve the efficiency of a catalyst are called promoters. For example, molybdenum acts as a promoter to increase the efficiency of the catalyst, iron, in the formation of ammonia gas from hydrogen and nitrogen.