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

* Sulfur dioxide (SO2): This is formed when sulfur impurities in petrol react with oxygen during combustion.

* Nitrogen oxides (NOx): These are formed when nitrogen in the air reacts with oxygen at high temperatures inside the engine.

Both sulfur dioxide and nitrogen oxides dissolve in atmospheric water to form sulfuric acid (H2SO4) and nitric acid (HNO3), respectively, which are the main components of acid rain.