We are asked to identify what type of rock would be formed in a plant-rich swamp. We all know that plant dies and the remain leaves in the soil called peat. Temperature, pressure and heat causes the remains to submerged under the soil bed layer and converts it into a waxy substance called kerogen. Kerogen then mixes with the rock under the soil bed layer to create what is called an oil shale. Oil shale is somehow similar to a coal. Both creates an energy when ignited. Therefore the correct answer to the question being asked is COAL or Oil Shale.
1) As for its chemical composition, coal is a mixture of high-molecular-weight polycyclic aromatic compounds, such as benzene C6H6, toluene C6H5CH3, xylene C6H4(CH3)2, naphthalene C10H8, anthracene C14H10, pyrene C16H10 and their derivatives with high mass fraction of carbon, as well as of water and volatile substances.
2) The coal asphaltenes have a relatively narrow MWD (full width ≈ 150 amu) with an average molecular weight of ≈340 amu. The petroleum asphaltenes display a broader MWD (full width ≈ 300 amu) and are heavier on average (≈680 amu).
~ I hope this helped, and I would appreciate Brainliest. ♡ ~ ( I request this to all the lengthy answers I give ! )