Which of the following substances would be considered toxic?

The correct choice identifies a substance that is capable of causing harm to living systems as toxic. Toxicity refers to the inherent capability of a substance to produce adverse effects on organisms, which can manifest in various forms such as damaging an organ, impairing physiological functions, or even leading to death. This definition encompasses a wide range of chemicals that can disrupt biological processes.

In contrast, a substance with no known effects on humans does not fit the definition of toxicity, as it does not present any risk or harmful potential. While a substance used in food production may be regulated and deemed safe for consumption, it doesn’t automatically imply that it is non-toxic. Similarly, a naturally occurring element in the environment can also be harmless or toxic, depending on its concentration and the exposure levels. Thus, the defining characteristic of toxicity is the potential to cause harm, making the identification of such substances crucial in any conversation about safety and health.