Draw a comparison among petrol, LPG and CNG as automobile fuels.

Explanation

Petrol is a fraction containing hydrocarbons with more than five carbon atoms (`C_5-C_(10)`). LPG contains butane as a major component with four carbon atoms. CNG contains methane with one carbon atom as a major component. With decrease in number of carbon atoms in the hydrocarbon, the calorific value increases and also the extent of incomplete combustion decreases. Therefore, the fuel efficiency increases. Apart from this, petrol contains sulphur and nitrogen which release harmful pollutants into the atmosphere, whereas LPG and CNG do not contain sulphur and nitrogen, Petrol being a liquid leaves residue in the engine. Among LPG and CNG, burning of CNG produces less amount of `CO_2` than LPG. Hence, CNG is considered as the best fuel.