Which type of adjuvant functions as a wetting agent and spreader?

The correct choice is a surfactant. This type of adjuvant is designed to reduce surface tension, allowing liquid products, like pesticides, to spread more evenly and adhere better to surfaces. Surfactants can improve the effectiveness of active ingredients by ensuring they penetrate and cover targeted areas more efficiently.

While emulsifiers function to stabilize mixtures of oil and water, stabilizers are typically used to maintain the consistency of a product, and dispersants help to keep solid particles evenly distributed in a liquid. These functions, while important in their contexts, do not primarily focus on enhancing wetting and spreading capabilities like surfactants do.