What is another example of a lethal gas aside from carbon monoxide?

Hydrogen cyanide is indeed another example of a lethal gas, making it the correct answer. It is a highly toxic chemical that can be found in certain industrial processes and is also a byproduct of combustion, especially in fires involving synthetic materials. The reason hydrogen cyanide is so dangerous is due to its ability to inhibit cellular respiration by preventing the body’s cells from using oxygen, leading to rapid unconsciousness and potentially death if exposure is significant.

In contrast, options such as nitrous oxide primarily act as anesthetics and are not considered lethal gases in the same way hydrogen cyanide is. Oxygen, while essential for life, is not toxic and does not fall under the category of lethal gases. Argon, a noble gas, is inert and does not chemically react with other substances, making it non-toxic as well. Thus, hydrogen cyanide stands out as a lethal gas due to its toxic effects on the body when inhaled or ingested.