Explanation:

- Coal tar: A thick black liquid produced during the destructive distillation of coal. It's not porous and is a mixture of various compounds.

- Bitumen: A viscous black material primarily derived from crude oil. Widely employed in road surfacing and roofing, it's unrelated to the pure form of carbon.

- Coal gas: A gaseous mixture largely consisting of hydrogen, methane, and carbon monoxide. Used historically as a fuel source.

- Coke: A tough, porous, and black substance. It's produced by carbonizing coal and is nearly pure carbon, widely used in metallurgy.

- Correct Answer: Coke