What is difference between leaded and unleaded petrol?

Answer 1

Leaded gas was used back in the days because it increases the octane rating of the gasoline and reduces whats called an "engine knock", basically it burns slower or less violently in the combustion chamber for a smoother combustion, however, leaded gas has lead particles in it which will stick to engine parts and come out into the air through the exhaust which is bad for modern emission controls like catalytic converters, and your lungs if you breath those lead particles... So they took the lead out of gasoline and put other anti-knock fuel additives with a smoother, "cleaner" burn like ethanol etc etc...