Which will cause an increase in the reaction rate between molecules?

See below ...

Explanation:

Rate of reaction is affected by 5 principle factors ...

Concentration of Reactants = > C

Surface Area = > A

Nature of Substance = > N

Temperature = > T

Catalysts = > C

FYI = > Notice this spells 'CANTC' (memory)

Changing any or all of the above may effect an increase rate of reaction. Specific details of how each accomplishes this is found in most college chem texts under Chemical Kinetics.