Which of the following combinations indicates an incorrect toxicity category?

The combination of "relatively non-toxic" with the label "caution" is inappropriate because the labeling conventions for toxicity categories are well-defined. Typically, products that are classified as relatively non-toxic should not require a caution label, which suggests that there is some level of risk associated with their use. Instead, such products would generally fall into a category that denotes they are safe for use without significant risk, often labeled as "no symbol" or "use as directed."

For the other combinations, "highly toxic" paired with a "warning" label is correctly reflective of the dangers associated with high toxicity substances, ensuring users are alerted to the need for careful handling. "Moderately toxic" with a "danger" label accurately communicates that there is a moderate level of hazard, which warrants caution during use. Finally, substances classified as "low toxicity" would typically have a corresponding label that indicates they are safe and may be used with minimal precautions rather than a cautionary term like "careful," which implies a higher level of risk.