Question

The crystalline forms of carbon are diamond, graphite and______.
A. Coal
B. Coke
C. Charcoal
D. Fullerene

Answer 1

Hint: Carbon is capable of existing in many allotropes of crystalline forms due to its valency which is four means it can share these four valence electrons to form four covalent bonds and can give different crystalline arrangements.

Complete answer:
Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, in same physical states known as allotropes of elements, they are actually the different structural modifications of an elements means the atoms of the elements are bonded together in a different manner compared to one another.
Carbon is capable of forming many allotropes due to its valency which is known as the combining capacity of an atom.
Well known allotropes of carbon include diamond, graphite and fullerenes.
In diamond form the carbon atoms are bonded together in form of a tetrahedral lattice arrangement means each carbon atom is covalently bonded to four other carbon atoms, this forms a strong, rigid, three dimensional structure.
In graphite form of carbon the atoms are bonded together in the sheets of a hexagonal lattice arrangement means each carbon atom is covalently bonded to three other carbon atoms, the carbon atoms are arranged in layers having strong bonds within each layer but only weak bonds between layers that's why graphite is relatively soft and slippery which makes it useful as a lubricant.
And in the fullerenes form(also known as bucky ball) the carbons atoms are bonded together in spherical, tubular or ellipsoidal formations and each sphere contains sixty carbon atoms in which each carbon atom is bonded to three other by single covalent bond but the bonds are relatively weak therefore fullerenes can dissolve and form solutions.

Hence the correct option is D.

Note: The term allotropy is used for elements only not for the compounds and it refers only to the different forms of an element within the same phase means either solid or liquid or gaseous state.