How can the rate of a reaction be increased?

Option (a) is correct.

Explanation:

A catalyst is a substance which helps in increasing the rate of a reaction without getting consumed. Therefore, the rate of a reaction can be increased by adding catalyst.

A decrease in temperature will decrease the average kinetic energy of reactant molecules. This will result into greater energy of the reactant molecules necessary for collision. Hence, the rate of reaction decreases as the energy of molecules increases.

At less surface area, rate of reaction will be limited as there will be less space for molecules to colloid.

By decreasing the amount of reactants, there will be less collisions between the reactants and hence, the rate of reaction will decrease.

Thus, it can be concluded that out of the given options only option (a) is correct.