consider the following reaction mechanism for the formation of nitrobenzene. Alright, so identify the reaction intermediate or intermediates and catalysts are catalysts. So, here, if we take a look all of this together represents our reaction mechanism. Each individual reaction represents our elementary step, right? So here this would be elementary step one. This would be elementary step to an elementary step three. Alright, so remember, a reaction intermediate appears first as a product, then later as a reactant. So, if we take a look here, let's try to find them. Let's see. So here, H two, N 03 appears as a product, and then later we see it appear as a reactant. So that would definitely be a reaction intermediate. But is that the only 1? We would say no, that's not the only one. Who else does that? Here's another one. C six, H six N 02 plus here. C 686 and 02 plus here, that is also a reaction intermediate. It appears first as a product and later as a reactant. Do we see any others? Yes, we see this. H. S. So four minus appears as a product and then later as a reactant. Now, do we have any catalysts? If we look, we do remember catalyst will appear in the very first step as a reactor. Then it will appear in the very last elementary step as a product. So, here, this would be our catalyst and that'd be our only catalyst involved in this entire reaction mechanism. So, just keep in mind a reaction intermediate appears first as a product and then later as a reactant. A catalyst appears as one of the first reactant, and then later in the very last elementary step. It appears as one of the products, so as long as you can remember that, who knows, the difference between a reaction intermediate and a catalyst?