Select the mechanisms where the concentration of the nucleophile/base has no effect on the reaction rate

Reactions in which the concentration of Nucleophile or Base has no effect on the rate of reaction depends only on the concentration of substrate. Such reactions are called Unimolecular Substitution or Elimination Reactions. The Kinetics of such reaction is First order with respect to substrate.

Examples:

SN¹ Reactions:
                        These are Unimolecular Substitution reactions. These are two step reactions in which the first step is the rate determining step. In RDS the substrate is ionized to generate a carbocation and is the slowest step. In second step the Nu attacks carbocation and is the fastest step.

E¹ Reactions:
                     These are unimolecular Elimination reactions. These are also two step reaction. In first step carbocation is generated (RDS step) and in second step the base abstracts proton to yield alkene. These reactions only depend on the concentration of substrate.

The answer is c : ) hope this answered your question!