The slow process of conversion of dead vegetation into coal.
Explanation
Carbonisation is the geological and thermochemical process responsible for the formation of fossil fuels, specifically coal, from ancient organic matter.
Option Analysis:
- The burning of coal in the presence of air to produce carbon dioxide. is Incorrect: The burning of coal in the presence of air is termed combustion. This is a rapid chemical reaction that produces carbon dioxide, heat, and light.
- The slow process of conversion of dead vegetation into coal. is Correct: Carbonisation is the slow process of conversion of dead vegetation into coal. Millions of years ago, dense forests were buried under the soil due to natural processes. As soil deposited over them, they were compressed. Under conditions of high temperature and high pressure inside the earth, and in the absence of air, dead plants were slowly converted into coal. Since coal is mainly carbon, this specific conversion process is named carbonisation.
- The industrial process of separating coke from coal tar. is Incorrect: The process of heating coal in the absence of air to obtain products like coke, coal tar, and coal gas is known as destructive distillation of coal.
- The extraction of pure carbon from petroleum products. is Incorrect: The extraction or separation of constituents from petroleum is achieved through fractional distillation, not carbonisation.
Key Takeaway:
Carbonisation is the slow, natural conversion of dead vegetation into coal under high pressure and temperature over millions of years.