What is a chemical’s mode of action?

A chemical's mode of action refers specifically to the mechanisms by which a pesticide interacts with a pest's biological processes to achieve its desired effect, such as killing or repelling the pest. This concept encompasses how the pesticide affects the target organism at a cellular or physiological level.

Understanding the mode of action is crucial for effective pest management, as it helps in selecting the right pesticides for specific pests, and can also inform approaches to minimize resistance development among pest populations. The other options provided, such as the physical state, price, or the chemical's reactions to temperature, do not pertain to how a pesticide operates within the biological systems of pests. Therefore, the focus on the biological impact of the pesticide in the correct answer exemplifies the essential understanding needed for effective pesticide application.