Correct answer:

The rate of reaction would decrease if the temperature of the reaction mixture was lowered because the molecules will have lower kinetic energy necessary for productive collisions.

Why?:

Collision theory models chemical reaction as being the result of reactant molecules colliding with each other. These collisions facilitate reactions by bringing reactants together and by providing kinetic energy that can serve as a source of activation energy for the reaction.  Higher temperatures increase the speed at which molecules move, making collisions more energetic and more likely to have sufficient kinetic energy to meet the reaction's activation energy. Lower temperatures at constant pressure might not decrease the number of collisions, but lower temperatures would lower the number of collisions that provide enough energy for the reaction to overcome the barrier of activation energy. Lower temperatures will lower the number of productive collisions.

Answering this question:

Always remember that for a product to form, the reactants must collide in such a way as to produce the right product. This is facilitated by proper orientation of colliding reactants and the efficiency of their collisions. A higher temperature increases the kinetic energy of molecules. In effect, there would be much more aggressive collisions which could form the products at a faster rate. If temperature is lowered, the molecules will be moving slower. Thus, it would take some time for a molecule to collide another molecule because of the slower speed. Formation of the products would also be slower.

So, the rate of reaction would decrease if the temperature of the reaction mixture was lowered because the molecules will have lower kinetic energy necessary for productive collisions.