How are sulfur oxides formed?

• A. Formed by combustion of nitrogen
• B. Produced by chemical interactions between sulfur and oxygen
• C. Dissolved in rainwater with no atmospheric reaction
• D. Produced by carbon dioxide reacting with water

Answer: (B)

Sulfur oxides form through oxidation of sulfur in the presence of oxygen. When sulfur-containing fuels burn, sulfur atoms react with oxygen at high temperatures to produce sulfur dioxide, and that gas can further react with oxygen to form sulfur trioxide. In the atmosphere, these oxides can dissolve in water droplets and react to form sulfurous and sulfuric acids, which leads to acid rain. The other statements don’t fit because nitrogen combustion produces nitrogen oxides, not sulfur oxides; sulfur oxides aren’t formed merely by carbon dioxide reacting with water; and saying they dissolve with no atmospheric reaction ignores the oxidative processes that generate and transform sulfur oxides in the air.