What is a species that forms during a reaction but is consumed along the process?

• A. Catalyst
• B. Reaction intermediate
• C. Endothermic
• D. Energy diagram

Answer: (B)

In a multi-step reaction, a species that is formed in one step and consumed in a later step is a reaction intermediate. It exists only temporarily as the mechanism moves from reactants to products and does not appear in the overall balanced equation. For example, in a two-step pathway A + B → X followed by X → P, the net reaction is A + B → P, while X is just a transient intermediate that is produced and then consumed.

This helps distinguish from a catalyst, which is not consumed and is regenerated after the reaction; from endothermic, which describes heat absorption or release rather than a species; and from an energy diagram, which is a graph of energy changes over the reaction rather than a particle.