[WhitneyRobinson]

When the concentrations of reactant molecules are increased,
The rate of reaction increases. The best explanation for this
Feature is the:

a. frequency of molecular collisions increases.
b. average kinetic energy of the molecules increases.
c. activation energy increases.
d. order of reaction increases.
e. none of the above are suitable explanations.

[Perito]

If the concentration of reactant molecules is increased, there will be more collisions between molecules in any given time.

b? There is nothing to suggest that the average kinetic energy increases. You'd have to heat it up to do that.

c? There's nothing to suggest that the activation energy increases. That will always be constant.

d? The order of reaction is based on the number of molecules that must collide. This will not change.