Answer: Option (a) is the correct answer.
Step-by-step explanation:
According to collision theory, more is the number of collisions more will be the rate of reaction, that is, more quickly product will be formed.
Therefore, when we increase the concentration of reactants then there will be increase in number of reactant molecules. Hence, more will be the reactant molecules more will be the collisions.
Thus, we can conclude that in the given reaction NaOH and HCl molecules collide more frequently at higher concentrations.