Question

The hardest form of carbon is:

• A. Coke
• B. Graphite
• C. Diamond
• D. Charcoal

Hint:

Compare the bonding structures of the different allotropes of carbon.

Answer 1

The Correct Option is C

Compare the bonding and structure of each option directly. Coke and charcoal are impure, amorphous forms of carbon obtained by heating coal or wood in the absence of air, they have no organized crystal lattice and end up as soft, brittle solids. Graphite has carbon atoms arranged in flat hexagonal sheets. Within one sheet the bonding is strong, but between the sheets the layers are held together only by weak van der Waals forces, which lets the layers slide over each other easily, so graphite feels slippery and is fairly soft. Diamond, on the other hand, has every carbon atom covalently bonded to four neighbours in a compact three dimensional network, with no weak layer anywhere in the structure. Because there is no direction along which the bonding is weak, diamond resists scratching and deformation from every angle, which is exactly why it is the hardest known natural material. So the correct choice is diamond, option C.