The opposite of a catalyst is a/an? Select one: a. anti-reactant b. anti-catalyst c. peroxide d. inhibitor

The correct answer is d. inhibitor.

Explanation:
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It works by lowering the activation energy needed for the reaction, allowing the reaction to proceed more quickly.

The opposite of a catalyst is a substance that slows down or prevents a chemical reaction. This substance is known as an inhibitor. Inhibitors work by increasing the activation energy or interfering with the reaction mechanism, thus reducing the reaction rate.

Anti-reactant: This term doesn't exist in chemistry.
Anti-catalyst: While this could conceptually mean something that opposes a catalyst, it's not a standard term.
Peroxide: Peroxides are a class of compounds, often reactive, but they are not generally considered inhibitors.
Inhibitor: This is the correct term for a substance that slows down or prevents a chemical reaction.