Which one is the hardest form of carbon ?

Coke
Graphite
Diamond
Charcoal

The correct answer is (c) diamond. Diamond is the hardest form of carbon, and is also the hardest natural substance on Earth. It is made up of carbon atoms that are arranged in a tetrahedral crystal structure. This structure gives diamond its strength and hardness.

Coke is a solid fuel made from coal. It is produced by heating coal in the absence of air. Coke is used in blast furnaces to make iron and steel.

Graphite is a form of carbon that is soft and flaky. It is used in pencils, lubricants, and electrodes.

Charcoal is a black, porous form of carbon that is produced by heating wood or other organic materials in the absence of air. It is used as a fuel, a preservative, and a filter.