Final answer:
The largest source of carbon monoxide pollution is motor vehicles, such as cars, trucks, and buses. Incomplete combustion of fossil fuels in these vehicles leads to CO emissions, which is a significant concern, especially in urban areas with dense traffic and industrial activities. The correct option is 3.
Step-by-step explanation:
The largest source of carbon monoxide pollution is motor vehicles. Carbon monoxide (CO) is a colorless, odorless gas that can be harmful when inhaled in significant quantities.
It is primarily released during the incomplete combustion of fossil fuels. Motor vehicles, including cars, trucks, and buses, are the major contributors to CO emissions outdoors.
Inside homes, sources such as gas stoves, unvented kerosene and gas space heaters, leaking chimneys and furnaces can release CO and affect indoor air quality.
While other sources like electric power plants, coal mining, and oil refineries do contribute to the emission of various pollutants, they are not the primary sources of carbon monoxide. The correct option is 3.