Which statement is true about a catalyst? a: a catalyst decreases the rate of the reaction. b. a catalyst is consumed during a chemical reaction. c. a catalyst lowers the activation energy of a reaction. d. a catalyst increases the reactant concentration during a reaction.

C. A catalyst lowers the activation energy of a reaction.

Explanation:

Catalyst increases the rate of the reaction without affecting the equilibrium position.Catalyst increases the rate via lowering the activation energy of the reaction.This can occur via passing the reaction in alternative pathway (changing the mechanism).The activation energy is the difference in potential energies between the reactants and transition state (for the forward reaction) and it is the difference in potential energies between the products and transition state (for the reverse reaction).in the presence of a catalyst, the activation energy is lowered by lowering the energy of the transition state, which is the rate-determining step, catalysts reduce the required energy of activation to allow a reaction to proceed and, in the case of a reversible reaction, reach equilibrium more rapidly.Catalyst does not consumed during a chemical reaction.

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So, the right choice is:

C. A catalyst lowers the activation energy of a reaction.