Based on process and environmental effects:-

petrol:- the air pollution will be caused because when use petrol for the vehicles, the vehicle release ore amount of CO2. it releases co2 more more than a volcano in a year.and it works good

cng:-  it causes less air pollution because when we use cng it releases less amount of co2 and it is also useful to use in kitchen , factory, works better than petrol..
2 3 2
no need
when some one else answers ur question beside of thank you u will see mark as best click it
ok f9 wil mark it