A mildly poisonous brown gas often found in smog and automobile exhaust fumes

• A. Larynx
• B. Maggot(s)
• C. Livor Mortis
• D. Nitrogen dioxide

Answer: (D)

Identifying common air pollutants by color and source helps you pin down the right contaminant. The brown, mildly poisonous gas found in smog and car exhaust is nitrogen dioxide. It is a reddish-brown gas produced by high-temperature combustion and is a key component of urban air pollution (NOx). Its presence explains why smog often has a brown tint and why exposure to exhaust fumes irritates the airways. The other options don’t fit because the larynx is an anatomical structure in the throat, maggots are insect larvae, and livor mortis is a postmortem change in blood distribution. Nitrogen dioxide is the gas specifically associated with that description.