What is a chemical substance that causes or increases the rate of a chemical reaction?

The correct answer is enzyme. Enzymes are biological catalysts that facilitate and accelerate chemical reactions within living organisms. They do this by lowering the activation energy needed for a reaction to occur, thereby increasing the rate of the reaction without being consumed in the process. Enzymes are crucial in various biochemical processes, including digestion and metabolism, making them essential for sustaining life.

Reagents, while involved in chemical reactions, do not specifically refer to substances that increase the rate of a reaction; they can be any substance used in a chemical reaction. Solvents are typically the medium in which reactions occur but do not inherently influence the rate of the reaction. Inhibitors, on the other hand, are substances that decrease the rate of a reaction by obstructing the activity of the enzyme involved. Therefore, the unique ability of enzymes to enhance reaction rates makes them the fitting answer to the question.