The correct answer is C. Fullerene.
Charcoal is a solid form of carbon that is produced by heating wood or other organic materials in the absence of air. It is a black, porous material that is used in a variety of applications, including fuel, water purification, and medicine.
Coke is a solid form of carbon that is produced by heating coal in the absence of air. It is a black, hard material that is used in a variety of applications, including iron and steel production, and as a fuel.
Fullerene is a type of carbon molecule that is composed of 60 carbon atoms arranged in a spherical shape. It is a relatively new material that has been studied for its potential applications in a variety of fields, including electronics, medicine, and materials science.
Carbon black is a fine, black powder that is produced by incomplete combustion of carbon-containing materials. It is used in a variety of applications, including rubber, plastics, and inks.
Fullerene is the purest form of carbon because it is composed of only carbon atoms. It is also the most stable form of carbon, and it has a number of unique properties that make it a promising material for a variety of applications.