Which chemical classification does NOT appear in the context of signal words for pesticides?

The classification that does not appear in the context of signal words for pesticides is "extremely toxic." Signal words are used on pesticide labels to provide information about the relative toxicity of a product to humans and the environment.

The terms "highly hazardous," "moderately hazardous," and "relatively safe" are used to categorize pesticides based on the level of danger they pose. "Highly hazardous" indicates a significant risk to human health and the environment, while "moderately hazardous" suggests a lower but still considerable risk. "Relatively safe" is often used to describe products that pose minimal risk when used according to label instructions.

In contrast, "extremely toxic" is typically not a standard classification used in signaling the level of hazard on pesticide labels. Instead, the existing classifications focus on providing clear and actionable information to help users understand the potential risks associated with different pesticides.