The process of formation of coal is called:

a) Fractional distillation

b) Carbonisation

c) Evaporation

d) Sublimation

The correct answer is (b) Carbonisation

The process of formation of coal from the remains of dead plants buried under the earth millions of years ago is called carbonisation. Thick forests were buried by natural processes (floods, earthquakes, sedimentation). In the absence of air, these plant remains were subjected to high pressure and high temperature deep inside the earth. Over geological time, the moisture and volatile components escaped, and the material became rich in carbon, finally turning into coal.

• Key idea: Plant matter → (pressure + heat + no air, very long time) → carbon-rich solid (coal)
• Stages often mentioned: peat → lignite → bituminous → anthracite (increasing carbon content and calorific value).

Do not confuse: Carbonisation (natural make-up of coal over time) vs. Destructive distillation of coal (industrial heating of coal without air to obtain coke, coal tar, coal gas).

Why are the other options incorrect

(a) Fractional distillation: Separation of petroleum into fractions by boiling points, not coal formation.

(c) Evaporation: Slow conversion of a liquid into vapour at the surface; unrelated to coal formation.

(d) Sublimation: Direct change of solid to gas (e.g., naphthalene, camphor), not how coal forms.