Final answer:
Rate a) does depend on the concentration of reactants.
Step-by-step explanation:
The question 'Rate _______ depend on the concentration of reactants.' can be completed with 'does' to indicate that the rate of a chemical reaction often depends on the concentration of reactants.
Considering a reaction where molecule A collides with molecule B to form product C, if the rate of the reaction is determined solely by the concentration of A and B in an elementary reaction, the rate will increase proportionally with an increase in concentration of the reactants. An increase in the concentration of A, for instance, would lead to more frequent collisions, thereby increasing the reaction rate.
However, for complex reactions, we must reference the rate law, which accounts for the reaction's order with respect to each reactant. This implies that changes in reactant concentrations might not result in a predictable change in rate without knowing the specific orders (m and n) which are determined experimentally.
Hence, the correct answer is Option A.