Which of the following substances is categorized as a pesticide?

The correct answer is herbicides, as they fall under the definition of pesticides, which are substances used to prevent, destroy, repel, or mitigate pests. Specifically, herbicides are designed to target and eliminate unwanted plants, commonly referred to as weeds. They work by interfering with the growth processes in plants, leading to their death. This targeting of specific plant species is a key characteristic of herbicides and aligns with the broader category of pesticides, which includes any chemical that manages pest populations.

Fungicides and insecticides are also categorized as pesticides, as they control fungi and insects respectively. Although fertilizers promote plant growth, they do not fit within the pesticide category because their primary function is not to control or manage pests. Thus, herbicides represent a specific type of pesticide focused on weed management.