The two gases that form from burning petrol in motor vehicles and contribute to acid rain are:

* Sulfur dioxide (SO₂): This is produced when sulfur impurities in the petrol are burned.

* Nitrogen oxides (NOx): These are formed from the reaction of nitrogen in the air with oxygen at the high temperatures within the engine.

These gases react with water, oxygen, and other substances in the atmosphere to form sulfuric acid and nitric acid, which fall to the earth as acid rain.