Which of the following is an example of a biological agent and toxin?

Ricin is correct as it is classified as a biological agent and toxin derived from the seeds of the castor bean plant. It is considered a highly toxic protein that can be fatal if ingested, inhaled, or injected. The toxicity of ricin is due to its ability to inhibit protein synthesis within cells, leading to cellular damage and, ultimately, death.

In contrast, the other options represent chemical agents rather than biological agents. Chlorine is a chemical element commonly used in disinfection and as a bleaching agent, while mustard gas and phosgene serve as chemical warfare agents that can cause severe harm through inhalation or skin contact but do not originate from biological sources. Understanding this distinction is crucial for identifying and managing hazards appropriately in hazmat situations.