Answer
The surface area of the reactants.
Explanation
The reactants of reaction III exists in both solid and liquid states, when solids and liquids react, increasing the surface area of the solid will increase the reaction rate. A decrease in particle size causes an increase in the solid’s total surface area.
Therefore, the only factor that would affect only the third reaction is:
The surface area of the reactants.
The last option is the correct answer.
