The rate of a chemical reaction in a cell is the measure of how a) often the reaction occurs. b) quickly the substrates are converted to product. c) much energy must be added for the reaction to occur. d) much activation energy is required for the reaction to occur. e) easily the reaction is inhibited.

B) quickly the substrates are converted to product

The chemical rate in a reaction is the measure of the speed of the colisions between the reactants atoms. The speed of the colision it's also the rate in which the substrates become products.

The activation energy has nothing to do with the rate of the reaction. It only considers the substance changes.