The addition of a catalyst to the reaction system.

Explanation

The correct answer for the effect of a catalyst on a reaction's rate is:(c) Increases the rate of forward but decreases the rate of backward reaction.Here's why the other options are incorrect:(a) Increases the rate of forward reaction only: While a catalyst does generally increase the rate of the forward reaction, it doesn't specifically affect only that direction. It typically affects both forward and backward reactions equally.(b) Increases the rate of reverse reaction: This is the opposite of what catalysts do. By lowering the activation energy for the forward reaction, they make it easier for reactants to form products, not for products to break down back into reactants.(d) Increases the rate of forward as well as backward reaction equally: This is true in a sense, but not entirely. A catalyst does affect both forward and backward reactions. However, its effect is usually greater on the forward reaction, leading to a net increase in the overall reaction rate.