Question

Assertion: Graphite is a good conductor of heat and electricity.
Reason: Graphite has all electrons firmly held together in C-C sigma bonds.
A.Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B.Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C.Assertion is correct but Reason is incorrect.
D.Both Assertion and Reason are incorrect.

Answer 1

Hint: We know that the diamond and graphite are both different allotropic forms of carbon. They vary in their structural arrangement and bonding and thus have different properties. Also, Graphite is the crystalline allotropes of carbon. Graphite has a layered structure.

Complete answer:
In diamond, each carbon atom is sp three hybridized and thus can form four bonds. It is bonded to four other carbon atoms in a tetrahedral arrangement forming a three- dimensional tetrahedral cage-like network structure. Layers of graphite are held by the weak van der wall’s force of attraction. Due to this structure, diamond is a hard and brittle material. All the four electrons of carbon are used up in bond formation and there are no free electrons in the network. Hence, it does not conduct electricity. Graphite has two dimensional structures. In graphite, only three of the four valence electrons of each carbon atom are involved in bonding.
Hence the fourth valence electron of each carbon atom remains unpaired or free. This free electron can easily move from one carbon atom to another carbon atom under the influence of applied potential. So, this free electron is responsible for the conduction of heat and electricity. Whereas, in graphite, each carbon atom is hybridized and forms three bonds. Each carbon atom is bonded to three other carbon atoms and thus, graphite has a layered sheet- like structure which makes it soft in nature. Only three out of the four valence electrons of carbon are involved in bond formation
Therefore, the correct answer is option C.

Note:
Remember that each layer is composed of planar hexagonal rings of carbon and each carbon atom makes three sigma bonds with three neighboring carbon atoms. The Fourth electron forms a pi bond.