Which of the following is a major source of oxides of nitrogen?

The correct choice highlights that high temperatures in car engines are a major source of oxides of nitrogen. In automotive engines, especially in combustion engines, the temperatures can exceed 1,500°C. At these high temperatures, nitrogen and oxygen from the air react to form various nitrogen oxides, including nitric oxide (NO) and nitrogen dioxide (NO₂). This reaction happens because the extremely high heat provides enough energy to break the strong bonds between nitrogen molecules, allowing them to react with oxygen.

While other sources such as bacterial activity in soil and incomplete combustion of fuels can produce nitrogen oxides, they are not considered major contributors compared to the emissions from vehicle engines. For instance, the bacteria in soil primarily produce nitrous oxide (N₂O) under specific conditions, but the quantities released are significantly less than those from vehicle emissions. Incomplete combustion typically results in carbon monoxide and unburned hydrocarbons; while it can also produce nitrogen oxides, the quantities are not as substantial as those generated in high-temperature combustion processes within engines. Decomposition of organic matter mainly contributes to the natural nitrogen cycle and the production of ammonium compounds rather than oxides of nitrogen.

Therefore, the conditions inside car engines provide a significant and well-documented source of