Which wording describes the combination of hazardous chemical substances that may require careful handling?

The correct choice highlights the specific terminology used in the field of hazardous materials and chemical handling. Pesticide mixtures refer specifically to combinations of various pesticide active ingredients or formulations that are blended for application. This requires careful management because mixing certain pesticides can lead to synergies that enhance efficacy or create hazardous reactions. Understanding pesticide mixtures is crucial for ensuring safe handling and application measures, as improper combinations could pose safety risks to handlers and the environment.

The other options, while related to chemistry, do not convey the same specificity regarding the handling of hazardous substances. Formulation blends imply a mix but are often used generically and don't emphasize hazards. Constituent elements refer to the individual parts of a compound, rather than the mixture itself. Chemical compounds denote broader categories of substances, lacking the needed focus on the unique considerations involved in mixing hazardous chemicals, particularly in the context of pesticides.