Why is sulfur undesirable in coal?

Sulfur is undesirable in coal primarily because it tends to corrode metal when burned. When coal containing sulfur is combusted, it forms sulfur dioxide (SO2), which can combine with moisture in the air to produce sulfuric acid (H2SO4). This acid can be corrosive to equipment and structures, leading to increased maintenance costs and potential damage to power plants and other facilities that rely on coal combustion.

Additionally, sulfur compounds contribute to the formation of acid rain, which has harmful effects on the environment, infrastructure, and human health. Therefore, managing the sulfur content in coal is crucial not only for the efficiency and safety of combustion systems but also for reducing its impact on the environment.

The other choices do not accurately represent the implications of sulfur in coal. Enhancing combustion efficiency or increasing energy output would suggest a positive effect of sulfur, which contradicts the known issues associated with its presence in coal. A claim that sulfur has no significant effect overlooks the serious consequences it poses to both machinery and the environment.