Concept:A reaction intermediate is a transient species formed and consumed within a reaction pathway.
Explanation:In a step-by-step reaction mechanism, certain species are produced in one elementary step.
These species are then used up in a later step to form the final products.
As a result, they do not appear in the overall balanced chemical equation.
Such species are called reaction intermediates.
For example, in the reaction
NO2+CO→NO+CO2, the species
NO3 is an intermediate because it is formed and then consumed.
Intermediates are present only along the reaction pathway, not in the original reactants or final products.
Answer:D. Intermediates