Many plants emit sulphur oxides. From where do these originate?

Sulphur oxides are primarily produced when fossil fuels that contain sulphur, such as coal or oil, are burned. When these sulphur-bearing fuels are combusted, the sulphur in the fuel reacts with oxygen in the air to form sulphur dioxide (SO2) and, in some cases, sulphur trioxide (SO3). This process is the main source of sulphur oxides in the environment and is particularly prominent in industrial operations.

The other choices do not accurately represent the origin of sulphur oxides. Sulphur precipitators are devices aimed at removing sulphur compounds from exhaust gases and do not generate them. Chemical additives used in boiler water may interact chemically but are not direct sources of sulphur oxide emissions. Similarly, while high-temperature combustion processes can produce various emissions, it is the combustion of specific sulphur-containing fuels that is the definitive origin for sulphur oxides.