Intermediate species means species that have 2 characteristics 1. they are a product in a previous step 2. they are consumed (they are reactants) in the following step Note that they must have both of these characteristics to be considered intermediates. If they have one or the other they are not counted as intermediates. Notice how NO is being produced in step I and being used up in step II. That is why it is an intermediate. Solution Intermediate species means species that have 2 characteristics 1. they are a product in a previous step 2. they are consumed (they are reactants) in the following step Note that they must have both of these characteristics to be considered intermediates. If they have one or the other they are not counted as intermediates. Notice how NO is being produced in step I and being used up in step II. That is why it is an intermediate..