Question

Which if the following causes least pollution when burnt:
a. Petrol
b. Natural Gas
c. Coal
d. Diesel

Answer 1

Hint: We shall be aware that the most efficient burning or combustible fuel is the one which is a complete hydrocarbon. The one which will burn with least pollution would be the one with the least amount of impurities.

Complete answer:
First of all, for simplicity sake, it should be understood that Natural Gas is more prominently methane with some other impurities. Natural gas is the simplest form of hydrocarbon and perhaps the cleanest burning fossil fuel. The chemical formula is $CH_4$.
1. Option c, which is Coal. We all know from our previous studies that there are primarily four different grades of Coal. But inadvertently, Coal is again another type of complicated compound with constituents containing Carbon, Oxygen, Nitrogen and Sulphur. So, the combustion of Coal would generate sulphur compounds along with other impurities, hence it is not the least pollution generating compound.
2. Option a, which is Petrol, Petrol is a more refined compound primarily used as fuel in transportation. It is produced through the distillation process of crude oil. Although it is more refined than diesel, it still contains a lot of impurities which are needed to be purified in order to make it a clean fuel. We know from our parents’ vehicles that the pollution generated are typically NOx and other such compounds which again makes it not the least polluting compound. ‘
3. Option d, which is diesel, again similar to petrol but even lesser refined. Hence, diesel is again not the least polluting compound.

Hence, the answer is (b) Natural Gas.

Note: It is to be noted that all of the above mentioned fuels’ combustion leads to some amount of pollution. It is the amount of impurities constituting the fuel which intensifies the magnitude of pollution. Natural gas in its compound form is methane with other minor impurities. The chemical formula of methane is CH4. Natural gas is obtained through extraction from oil wells.