Which substance is classified as a pulmonary (choking) agent?

Chlorine is classified as a pulmonary (choking) agent because it primarily affects the respiratory system. When inhaled, chlorine gas can cause damage to the lungs and airways, leading to symptoms such as coughing, throat irritation, and difficulty breathing. Its mechanism of action involves the formation of hydrochloric acid upon contact with moisture in the respiratory tract, resulting in severe irritation and injury to lung tissue.

In contrast, mustard gas is primarily a vesicant, which means it causes severe blistering and damage to skin and mucous membranes rather than being classified as a pulmonary agent. Sarin is a nerve agent that disrupts the functioning of the nervous system, leading to a completely different set of symptoms, and vesicant agents are typically associated with causing skin burns and blisters rather than directly affecting the respiratory system as chlorine does. Therefore, chlorine specifically fits the definition of a choking agent due to its targeted damage to pulmonary function.