Which of the following is an example of an adjuvant?

An adjuvant is a substance that is added to a pesticide formulation to enhance its effectiveness or improve its application. In this case, a penetrant is a type of adjuvant that helps improve the absorption of a pesticide into the target organism or the surface it is meant to affect. By facilitating better penetration, penetrants can increase the efficacy of the active ingredient in overcoming barriers that might otherwise limit its performance.

Other options listed have distinct roles within pesticide use. Organophosphates refer to a specific class of chemicals primarily used as insecticides and do not serve the additional role of enhancing other pesticide effects. Biopesticides are derived from natural materials and act as pesticides themselves, while herbicides are specifically aimed at controlling unwanted plants. Neither biopesticides nor herbicides functions as adjuvants; rather, they serve as active ingredients with particular targets in pest management.