Question

a substance that influences the reaction but does not participate in the reaction is a

catalyst
reactant
product
substrate

Explanation:

To solve this, we analyze each option:

• Catalyst: A catalyst speeds up (or slows down) a chemical reaction without being consumed (not participating in the reaction as a reactant or product).
• Reactant: A reactant is a substance that participates in and is consumed during a reaction.
• Product: A product is formed from reactants during a reaction, so it participates in the sense of being the result.
• Substrate: A substrate is a reactant in a biochemical reaction (like in enzyme - catalyzed reactions), so it participates.

So the substance that influences the reaction but does not participate is a catalyst.

Answer:

A. catalyst