Which one is not an crystalline allotrope of carbon ?

Question

Accepted Answer

Explanation:

1. **Coal** (Option 1): Coal is not a crystalline allotrope of carbon. It is an amorphous form of carbon, meaning it lacks a well-defined crystalline structure. Coal is primarily composed of carbon, but it also contains other elements such as hydrogen, sulfur, oxygen, and nitrogen. Its structure is disordered, which is characteristic of amorphous materials. This lack of a regular, repeating pattern distinguishes coal from crystalline allotropes of carbon.

2. **Graphite** (Option 2): Graphite is a crystalline allotrope of carbon. It has a layered structure where carbon atoms are arranged in a hexagonal lattice. These layers are held together by weak van der Waals forces, allowing them to slide over each other easily, which is why graphite is used as a lubricant and in pencils. The regular arrangement of carbon atoms in graphite qualifies it as a crystalline form of carbon.

3. **Diamond** (Option 3): Diamond is another crystalline allotrope of carbon. In diamond, each carbon atom is tetrahedrally bonded to four other carbon atoms, forming a very strong and rigid three-dimensional lattice. This structure gives diamond its renowned hardness and high refractive index. The orderly and repeating pattern of carbon atoms in diamond makes it a crystalline material.

4. **Fullerene** (Option 4): Fullerene is also a crystalline allotrope of carbon. Fullerenes are molecules composed entirely of carbon, taking the form of a hollow sphere, ellipsoid, or tube. The most well-known fullerene is buckminsterfullerene (C60), which resembles a soccer ball. The carbon atoms in fullerenes are arranged in a highly symmetrical and regular pattern, characteristic of crystalline structures.

In summary, coal is the only option that does not have a crystalline structure, making it the correct answer as the non-crystalline allotrope of carbon. Graphite, diamond, and fullerene all have well-defined crystalline structures, distinguishing them from coal.