Among the following motor vehicle fuels, which one is considered the greatest polluter?

Gasoline is considered the greatest polluter among the listed motor vehicle fuels due to its chemical composition and the emissions produced during its combustion. When gasoline burns, it releases a range of pollutants, including carbon monoxide, nitrogen oxides, volatile organic compounds (VOCs), and particulate matter. These pollutants contribute significantly to air quality issues, including smog formation and respiratory problems in humans.

Diesel fuel, while also a contributor to air pollution, tends to emit pollutants differently. It generally produces more nitrogen oxides and particulate matter than gasoline, but modern diesel engines have advanced emissions control technologies that can reduce these emissions significantly.

Ethanol, derived from renewable sources, is often seen as a cleaner alternative. Although it generates some emissions, the overall environmental impact is less severe than that of gasoline, particularly regarding greenhouse gases.

Natural gas is the cleanest-burning fossil fuel among the options listed. It produces fewer emissions of carbon dioxide and other harmful pollutants compared to gasoline and diesel.

Overall, gasoline's extensive use and the resultant emissions make it a significant contributor to air pollution, positioning it as the greatest pollutant in this context.