Petrol used in cars is obtained by refining ?​

Crude oil is refined to make petrol (in America this is known as gasoline) or diesel. Most forms of transport use either petrol or diesel to power their engines - from lawnmowers, cars, buses and motorbikes to large ships and aeroplanes.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.