Which of the following is an example of a chemical warfare agent?

Sarin gas is classified as a chemical warfare agent due to its characteristics and intended use in harmful applications. It is a potent nerve agent that disrupts the normal functioning of the nervous system, leading to serious health effects or death when exposure occurs. Sarin is a synthetic chemical compound with a high level of toxicity and is designed specifically for use in military operations to incapacitate or kill enemy personnel.

While chlorine gas can also be used in warfare and has been weaponized in certain conflicts, it is primarily known as a toxic industrial chemical rather than a specific military-grade agent. Ammonia and carbon monoxide, on the other hand, are commonly found in various industrial and environmental contexts and do not fit the definition of a chemical warfare agent intended for use in warfare settings.

Therefore, sarin gas stands out as the most appropriate answer when considering the criteria for a chemical warfare agent, particularly due to its design for use as a weapon and its specific classification and regulation under various international treaties regarding chemical weapons.