Define 'pesticide'.

A pesticide is defined as a substance specifically formulated for the purpose of preventing, destroying, repelling, or mitigating pests. This includes a wide range of organisms that can adversely affect crops, livestock, or human health, such as insects, weeds, fungi, and bacteria. The emphasis on prevention and destruction is critical, as the primary role of pesticides is to manage pest populations and protect agricultural resources effectively.

In this context, the distinction is clear: while substances that might improve crop growth or are found in plants may have beneficial applications in agriculture, they do not fall under the specific definition of a pesticide. Moreover, synthesized compounds for agricultural use can often refer to a broader category that includes fertilizers or non-pesticidal chemicals, which again diverges from the targeted role of pesticides. Therefore, option B precisely captures the intended use and definition of pesticides in agricultural practices.