Which of the following describes a biological toxin?

A biological toxin is specifically defined as a poison that is produced naturally by living organisms. These organisms can include a wide range of life forms, such as plants, animals, fungi, and bacteria. The toxins they produce can have various harmful effects on other organisms, including humans, often as a means of defense or to capture prey.

The other choices refer to different categories of harmful substances. A compound created through chemical synthesis involves artificial production and does not fit the definition of a toxin produced by living organisms. A natural mineral with harmful effects describes inorganic substances rather than biologically-derived toxins. Similarly, a synthetic drug is designed for therapeutic purposes and is not a biological toxin; it may be made to help treat conditions rather than harm. Thus, the correct response emphasizes the biological origin and natural production of the toxin.