Question

why petrol float on water

Answer 1

Because Petrol has lesser density than water

For an idea,
1 litre of water weighs 1kg
whereas
1 litre of petrol weighs 0.77kg
less weight less dense

"Same volume of different substance differ by their weights"

Answer 2

Heya✌️✌️☺️☺️☺️..
Petrol floats on water as the oil and gas are generated depending on local conditions, petroleum products sperates by density oil is less dense than water so it 'floats' on water