The correct answer is: C. diamond
Diamond is a crystalline allotrope of carbon with a diamond cubic crystal structure. It is the hardest naturally occurring substance and is widely used as an abrasive. Diamond is also used in jewelry and other decorative items.
Graphite is an allotrope of carbon that is composed of flat sheets of carbon atoms arranged in a hexagonal lattice. Graphite is a soft, slippery material that is used in lubricants, brake pads, and other applications.
Carbon nanotubes are cylindrical allotropes of carbon with a diameter of typically 1â100 nanometers and a length of up to several micrometers. Carbon nanotubes are extremely strong and lightweight, and have a wide range of potential applications in electronics, materials science, and other fields.
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. Fluorine is the most electronegative element and is extremely reactive, forming compounds with most elements. Fluorine is used in a variety of industrial applications, including the production of hydrofluoric acid and fluorine-containing refrigerants.
In conclusion, the correct answer is diamond. Diamond is a crystalline allotrope of carbon with a diamond cubic crystal structure. It is the hardest naturally occurring substance and is widely used as an abrasive. Diamond is also used in jewelry and other decorative items.