What poisonous gas is primarily found in auto exhaust?

The correct answer is carbon monoxide. This poisonous gas is a byproduct of the incomplete combustion of fossil fuels, commonly present in the exhaust of internal combustion engines in vehicles. When fuel does not burn completely, carbon monoxide is produced, which is hazardous because it can bind to hemoglobin in the blood more effectively than oxygen, leading to reduced oxygen delivery throughout the body. This makes carbon monoxide particularly dangerous in enclosed spaces where vehicle exhaust can accumulate, posing a serious risk to health.

While hydrogen sulfide, carbon dioxide, and nitrogen dioxide are also gases associated with vehicle emissions or combustion, they play different roles and often come from different sources. Hydrogen sulfide is typically associated with industrial processes and natural gas, carbon dioxide is a normal byproduct of complete combustion and is not poisonous in typical scenarios, and nitrogen dioxide is primarily formed through high-temperature combustion, particularly in gasoline engines, but is not the main poisonous gas associated with auto exhaust.