Question

ASSERTION : Graphite is soft while diamond is hard.
REASON : Graphite has three dimensional structure while diamond has planner.
A. Both assertion and reason are correct and reason is the correct explanation for assertion
B. Both assertion and reason are correct and 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: Allotropy is the existence of a chemical element in two or more forms, which may differ in the arrangement of atoms in crystalline solids or in the occurrence of molecules that contain different numbers of atoms. Allotropes are different structural forms of the same element and can exhibit quite different physical properties and chemical behaviors.

Step by step answer:Carbon is capable of forming many allotropes due to its valence. Well-known forms of carbon include diamond and graphite
The assertions tell that graphite is soft and diamond is hard. Currently, diamond is regarded to be the hardest known material in the world hence it is a correct statement.
 In graphite carbon atoms form planar, hexagonal rings to give it a sheet like structure. Each sheet is joined to each other by a weak van der Waal force. Hence diamond is harder than graphite. Hence the reason is incorrect.

Therefore, option (C) is correct.

Additional Information: Graphite can conduct electricity because of the delocalized (free) electrons in its structure. These arise because each carbon atom is only bonded to 3 other carbon atoms. This leaves 1 electron to become delocalized. However, in diamond, all 4 outer electrons on each carbon atom are used in covalent bonding, so there are no delocalized electrons.

Note: it is confusing for students to understand the electrical conducting behavior diamond and graphite both are made up of carbon. Here students have to carefully remember that graphite is a good conductor of electricity.