Which of the following is NOT a factor that affects the rate of reaction?

The rate of a chemical reaction can be influenced by several factors that directly impact how reactants interact with each other. The surface area of solid reactants plays a crucial role; increased surface area exposes more particles for collision, thereby enhancing the reaction rate. Temperature is another critical factor, as higher temperatures increase the kinetic energy of particles, leading to more frequent and effective collisions. Additionally, when dealing with gases, pressure can affect reaction rates; increasing pressure increases the concentration of gas molecules, resulting in a higher frequency of collisions.

In contrast, the time of day does not have a direct effect on the fundamental aspects of the reaction, such as the energy of the particles, concentration, or surface area. While the time of day may influence ambient conditions such as temperature or light, it is not a variable that impacts the intrinsic chemistry of the reactants directly. Thus, this choice is the one that does not belong among those that genuinely influence the rate of chemical reactions.