Which concept describes something that decreases the rate of a reaction or halts it?

• A. Catalyst
• B. Acid
• C. Inhibitor
• D. Base

Answer: (C)

Inhibition is the idea being tested. An inhibitor is a substance that slows down or stops a reaction by interfering with how the reaction proceeds—such as by blocking reactive sites, binding to reactants or catalysts, or changing conditions so fewer effective collisions happen. This is why an inhibitor best fits something described as decreasing the rate or halting a reaction.

Catalysts do the opposite: they speed up reactions by providing an easier pathway. Acids and bases alter the reaction environment and can affect rate, but they’re not defined by consistently decreasing the rate; they may speed up or slow down depending on the situation.