Which of the following is an example of a blood agent?

Cyanogen chloride is classified as a blood agent due to its mechanism of action in the body. Blood agents are toxic chemicals that interfere with the body's ability to use oxygen, effectively preventing cellular respiration. When cyanogen chloride is inhaled, it rapidly enters the bloodstream and binds with hemoglobin, which inhibits the blood's capacity to transport oxygen. As a result, it can lead to suffocation and eventual organ failure if exposure is significant and immediate intervention is not provided.

This classification is essential for understanding the potential threats posed by various chemical agents and aids in developing appropriate response strategies during chemical incidents. Other options do not fall into the category of blood agents. For instance, ricin is a toxic protein derived from castor beans and operates differently in the body, plutonium is a radioactive element with different health hazards, and dengue fever is a viral infection transmitted by mosquitoes, neither of which meet the definition of a blood agent.