Which of the following can act to alter the rate without being consumed in the overall reaction?

• A. Reactant
• B. Product
• C. Temperature
• D. Catalyst

Answer: (D)

A catalyst changes the rate by providing an alternative pathway with lower activation energy, so more molecules can react per unit time at the same temperature. It participates in the mechanism but is not consumed; after the reaction finishes, its amount is unchanged, so it does not appear in the overall equation. That’s why it uniquely fits the idea of altering rate without being consumed. Reactants are consumed, products are formed, and temperature is a condition, not a substance that participates like a catalyst.