The residue left after destructive distillation of coal is:

a) Coal tar

b) Coke

c) Ammoniacal liquor

d) Water gas

The correct answer is (b) Coke

Destructive distillation of coal means heating coal strongly in the absence of air. The coal breaks down into several useful products. The solid residue that remains in the chamber is called coke. It is porous, almost pure carbon, burns with little smoke, and is used as:

• a reducing agent in extraction of metals (e.g., iron in blast furnace),
• a fuel in industries,
• a source for making water gas (by passing steam over red-hot coke).

What other products come out?

• Coal tar (liquid fraction): thick, black liquid containing many chemicals (e.g., naphthalene, phenol, toluene) used for dyes, drugs, explosives, perfumes.
• Ammoniacal liquor (aqueous): water containing ammonia, used to make ammonium salts (fertilizers).
• Coal gas (gaseous mixture): mainly H₂, CH₄, CO, used as a fuel.

Why the other options are not the residue

• (a) Coal tar: liquid by-product, not the solid residue.
• (c) Ammoniacal liquor: aqueous by-product, not the residue.
• (d) Water gas: a separate fuel gas (CO + H₂) made later by passing steam over hot coke—it is not a direct product/residue of the destructive distillation step.