Which of the following is NOT a type of biological agent?

The correct answer highlights that the mustard agent is not classified as a biological agent. Instead, it is a chemical warfare agent. Biological agents are typically living organisms or pathogens, such as bacteria, viruses, or toxins produced by those organisms, which can cause diseases in humans, animals, or plants.

Anthrax, for example, is caused by the bacterium Bacillus anthracis and is a well-known biological threat. Ebola is a virus that leads to a serious hemorrhagic fever, making it another clear example of a biological agent. Typhus, caused by Rickettsia bacteria, also falls under the category of biological agents since it involves pathogenic organisms that can spread diseases.

In contrast, the mustard agent, specifically mustard gas or sulfur mustard, is a synthetic chemical compound known for its use in chemical warfare. It does not originate from living organisms and does not exert its effects through biological paths, which distinguishes it from true biological agents. This context provides clarity on why mustard agent is not included in the category of biological agents.