Answer:
Option D. the frequency of molecular collisions increases
Step-by-step explanation:
Collision theory states that for a reaction to occur, the reactant particles must collide with the right orientation. With this knowledge, increasing the concentration of the reactants will increase the rate of the reaction as the reactant particles will collide frequently because the reactant particles are entirely every in the reaction vessel. This create room for easy collisions which in turn speed up the reaction rate.