Question

Which of these is not a fossil fuel?
A. Coal
B. LPG
C. Biogas
D. All are fossil fuels

Answer 1

Hint: We know by the definition of fossil fuel that fossil fuels are derived from decomposing plants and animals. Fossil fuels are formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing organic molecules that release energy in combustion.

Step by step answer:
From the definition we know that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in the Earth's crust over millions of years. Aquatic phytoplankton and zooplankton that died millions of years ago and sediment in large quantities under conditions like with no oxygen began forming petroleum and natural gas as a result of anaerobic decomposition. Terrestrial plants, on the other hand, tended to form coal and methane.
So from the above definition of fossil fuels we can easily answer our question.
We have Coal, LPG and Biogas as our options. We know that coal is formed by the dead remains of terrestrial plants and animals. So coal is a fossil fuel.
Now our next option is LPG. LPG is Liquefied Petroleum Gas. LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. So now we can say that LPG is also a fossil fuel as it is derived from fossil fuel sources.
Now we come to the only remaining option that is biogas. We can produce biogas at our home by anaerobic degradation of animal waste such as cow dunk in presence of water. Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide.
One reason that we do not include biogas as fossil fuel is because fossil fuels are ultimately a hydrocarbon fuel and as hydrocarbon fuel they come in many different forms after purified or refined. Biogas is also a hydrocarbon fuel, but generally speaking biogas is not a fossil fuel because it was not mined and captured from a geological deposit. And it is made by humans in artificial conditions. If we let any organic matter rot in concentrated conditions it's going to produce methane plus several other “thanes" like butane and propane.
So from the above discussion, we now came to our conclusion that biogas is not as fossil fuel.
So, our answer is option C.

Note: We should know that fossil fuels are of great importance because they can be burned (oxidized to carbon dioxide and water), producing significant amounts of energy per unit mass. Coal was used to run furnaces for the smelting of metal ore. Natural gas deposits are also the main source of helium.
We should know that Phytoplankton are aquatic plants; Zooplankton are small aquatic animals. Phytoplankton depends on sunlight for making their food; they primarily live on the surface of the water, while zooplankton lives in the darker and colder area of the water body. They formed petroleum and natural gas when they died millions of years ago and got sediment in conditions like with no oxygen.