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Many fuels that are used to automobiles contains lead.

This becomes very dangerous to human health at it releases toxic substances.

To avoid this danger presently petrol that do not contain lead is used as fuels and are called as unleaded petrol.

They cause no damage to health.

Gasoline is an example of unleaded petrol.
Many fuels are extracted from the earth's crust.All of these fuels contains lead.If lead is seperated from the petrol then it is called as unleaded petrol.