Understanding Carbon Allotropes and Their Properties

This question asks us to identify the statement that is NOT correct regarding the properties and structures of different forms (allotropes) of carbon: Diamond, Fullerene, and Graphite. Let's analyze each statement.

Diamond Hardness and Covalent Bonding

Statement 1: Diamond is hard due to extended covalent bonding in it

This statement is correct. Diamond has a giant covalent structure. Each carbon atom is covalently bonded to four other carbon atoms in a rigid, three-dimensional tetrahedral lattice. These covalent bonds are very strong and require a lot of energy to break. This extensive network of strong bonds is what makes diamond exceptionally hard.

Fullerene Structure: Rings Composition

Statement 2: Fullerene is composed of five and six membered rings

This statement is correct. Fullerenes are a distinct class of carbon allotropes. The most famous fullerene is C60 (buckminsterfullerene), which has a structure resembling a soccer ball. This structure is made up of pentagons (five membered rings) and hexagons (six membered rings) fused together. The presence of these specific ring types is characteristic of fullerene structures.

Diamond Electrical Conductivity: An Insulator

Statement 3: Diamond is a good conductor of electricity

This statement is NOT correct. In diamond, all valence electrons of the carbon atoms are involved in forming strong covalent bonds. These electrons are localized within the bonds and are not free to move throughout the structure. Because there are no mobile charge carriers (like free or delocalized \(\text{e}^-\)), diamond cannot conduct electricity and is actually a very good electrical insulator.

Graphite's Lubricant Properties

Statement 4: Graphite is used as a lubricant

This statement is correct. Graphite has a unique layered structure. Each layer consists of carbon atoms arranged in hexagonal rings, similar to a sheet of chicken wire. Within these layers, carbon atoms are held together by strong covalent bonds. However, the forces between the layers are weak van der Waals forces. This allows the layers to easily slide past one another, giving graphite a slippery feel and making it effective as a lubricant, especially under conditions where oil-based lubricants might fail.

Conclusion: Identifying the Incorrect Statement

Based on the analysis of each statement:

• Statement 1 is correct (Diamond hardness).
• Statement 2 is correct (Fullerene structure).
• Statement 3 is incorrect (Diamond conductivity).
• Statement 4 is correct (Graphite lubricant).

Therefore, the statement that is NOT correct is: "Diamond is a good conductor of electricity".