The calorific values of petrol and CNG are 45,000 kJ/kg and 50,000 kJ/kg, respectively

Explanation:

Calorific value fuel efficiency is directly proportional to calorific value.
A higher calorific value leads to the higher efficiency of fuel.
A higher calorific value also leads to the complete combustion of fuel(lesser environmental pollution).

By the above-mentioned points we can state that we will prefer to use CNG fuel in a vehicle.