Match the correct chemical term with its definition: Catalyst.

The correct choice for the definition of "catalyst" is B, which describes its role in influencing the rate of a chemical reaction. A catalyst is a substance that accelerates a chemical reaction without being consumed in the process. It achieves this by providing an alternative pathway with a lower activation energy for the reaction to proceed. Importantly, while catalysts do speed up reactions, they do not slow them down; their primary function is to enhance the reaction rate.

The other options do not accurately represent the role of a catalyst:

• The option indicating that it slows down a chemical reaction is incorrect because catalysts are only associated with increasing reaction rates.

• The option suggesting that it prevents polymerization pertains to inhibitory agents, not catalysts.

• Finally, the mention of yielding oxygen is unrelated to the definition of a catalyst and instead pertains to substances participating in oxidation or reduction reactions.

Therefore, the role of a catalyst is best captured by its ability to speed up a chemical reaction, affirming that option B is the most accurate definition.