Which of the following is considered a harmful substance?

Toxins are classified as harmful substances because they can cause negative effects on health and the body when ingested or exposed to. They are often harmful in both small and large quantities and can lead to various health issues depending on their nature and concentration. For instance, certain toxins can disrupt bodily functions, lead to poisoning, or result in chronic health conditions with long-term exposure.

In contrast, nutrients and vitamins are essential for maintaining health and promoting growth and development. They play critical roles in bodily functions, such as metabolism and immune support. Water, while necessary for life, helps regulate body temperature, aids digestion, and facilitates cellular processes. Unlike toxins, these substances contribute positively to our overall well-being when consumed in appropriate amounts.