Answer:
Sulfur oxides
Explanation:
Sulfur oxides (mainly sulfur dioxide in this case) are produced when fossil fuels are burnt in industrial sources like power stations, factories, incinerators etc, as most fuels sulfur as impurities. Sulfur reacts with the oxygen in the air during combustion, thus giving off sulfur dioxides.
When these sulfur dioxide reacts with the rainwater (or water vapor in the atmosphere), they form sulfurous acid, or even sulphuric acid if sulphurous acid further reacts with oxygen. These acids cause the rain to become more acidic than normal.
The reaction is outlined below:
SO2(g) + H2O(l) ⇌ H2SO3(aq)
The reason why carbon dioxide isn't the correct answer (as CO2 is an acidic gas too) is because rain should naturally be slightly acidic (pH 5.6) due to carbon dioxide reacting with rainwater to form carbonic acid. Speaking of the harm of carbon dioxide, it should not be classified as a pollutant generally.
