Q1: Which of the following materials has the poorest electrical conductivity ?

ANS:A - Carbon

Carbon, in its various forms, can exhibit a wide range of electrical conductivity, depending on its structure and bonding configuration:

1. Diamond: Diamond, a crystalline form of carbon, is an electrical insulator. It consists of carbon atoms arranged in a tetrahedral lattice structure, where each carbon atom is bonded to four other carbon atoms through strong covalent bonds. These strong bonds result in a lack of free electrons, making diamond a poor conductor of electricity.
2. Graphite: Graphite, another allotrope of carbon, is a good conductor of electricity. In graphite, carbon atoms are arranged in layers of hexagonal rings, with weak van der Waals forces holding the layers together. Within each layer, each carbon atom is bonded to three others, forming a delocalized π-electron system. This delocalization allows for the movement of electrons along the layers, giving graphite its high electrical conductivity. Graphite is commonly used in applications where high electrical conductivity is desired, such as in electrodes, electrical contacts, and in the production of pencils (where it serves as the "lead").
3. Carbon fibers: Carbon fibers are highly conductive along the fiber axis due to the sp² hybridization of carbon atoms and the delocalization of π-electrons within the fibers. However, their overall conductivity can vary depending on factors such as fiber alignment and orientation.
4. Amorphous carbon: Amorphous carbon, which lacks a well-defined crystalline structure, can exhibit a range of electrical conductivities depending on its composition and structure. Some forms of amorphous carbon, such as activated carbon, are relatively poor conductors of electricity due to their highly porous nature and disordered structure.

In summary, while diamond is an electrical insulator, graphite and certain forms of carbon, such as carbon fibers, can be good conductors of electricity due to their specific structures and bonding configurations. Therefore, the electrical conductivity of carbon can vary significantly depending on its allotrope and form.