On which of the following factor the rate at which a substance react…

 The factor on which the rate at which a substance reacts depends is the "active mass" or "concentration of reactants."

The active mass, or concentration, of the reactants is a key factor that influences the rate of a chemical reaction. An increase in the concentration of reactants generally leads to a higher reaction rate. This is because a higher concentration results in a greater number of reactant particles per unit volume, increasing the frequency of collisions between reactant molecules. With more frequent collisions, there is a higher probability of effective collisions—those with sufficient energy and proper orientation to result in a reaction. As a result, the rate of the reaction increases.

It is important to note that the term "active mass" is an older term that has been largely replaced by the concept of concentration. In modern chemistry, the concentration of reactants is used to describe the amount of reactant per unit volume or per unit of space. However, the fundamental principle remains the same: an increase in the concentration of reactants generally leads to an increase in the rate of a reaction.