Which gas is listed as a toxic gas?

• A. Oxygen
• B. Nitrogen
• C. Chlorine
• D. Argon

Answer: (C)

Gases classified as toxic can cause harm to health through inhalation or contact even at relatively low exposures. Chlorine is a toxic gas because inhaling it irritates the eyes, nose, and lungs and can lead to coughing, shortness of breath, and more severe respiratory damage; at higher concentrations it can be life-threatening. It also reacts with moisture in the air to form acids that damage tissue. In contrast, oxygen is essential for life and isn’t toxic at normal levels (though extreme conditions can cause problems), while nitrogen and argon are inert gases that aren’t toxic themselves (though they can displace oxygen and create an asphyxiation risk).