What characterizes a substance defined as a poison based on its LD50 values?

A substance is classified as a poison based on its toxicity levels, specifically its LD50 values, which represent the lethal dose required to kill 50% of a test population. The designation of "poison" reflects a higher level of toxicity, which is characterized by lower LD50 values.

When considering the correct option, a substance that has an oral LD50 value of less than 100 mg per kg indicates it is highly toxic, as only a small amount is required to produce lethal effects. Furthermore, the dermal LD50 value of less than 500 mg per kg also reinforces this classification, as it suggests that significant exposure through the skin can lead to serious toxicity.

This strong emphasis on the low LD50 values in both oral and dermal routes of exposure is what characterizes a substance as poisonous. It illustrates that even small doses can be hazardous. Thus, substances with both oral LD50 less than 100 mg/kg and dermal LD50 less than 500 mg/kg are recognized as poisons due to their significant potential for harm with relatively low doses.