Which of these statements is true
a. chemical reactions can be slowed down by increasing the temperature.
b. once a chemical reaction gets started, the reacting particles no longer have to collide for products to form.
c. enzymes are biological catalysts.

Answer : Option C) Enzymes are biological catalysts.

Explanation : Enzymes are those compounds which lowers the activation energy of any given reaction. From the definition of the catalyst, it is a chemical which increases the rate of a chemical reaction without itself actually involved in the reaction.

The fact that enzymes aren't the ones which participate in a reaction distinguishes catalysts from substrates, which are the reactants on which catalysts work. Enzymes catalyzes most of the biochemical reactions.

Therefore, this statement is true for enzymes. They are biological catalysts.