Final answer:
Sulfur oxides in flue gas are undesirable because they contribute to the formation of acid rain, which harms ecosystems and corrodes monuments and buildings.
Step-by-step explanation:
Sulfur oxides are undesirable in flue gas because they contribute to acid rain. When sulfur dioxides (SO2) and other sulfur oxides (SOx) are emitted into the atmosphere, they can react with water vapor to form sulfuric acid. This acid rain can have detrimental effects on both the natural environment and man-made structures, damaging ecosystems, lowering the pH of lakes, and corroding buildings and monuments. Industrial efforts to minimize the release of SOx, like using scrubbers in coal-burning power plants to trap SO2 by reacting it with lime to produce calcium sulfite dihydrate, are important in reducing acid rain.