Question

Assertion :
Diamond is the hardest crystalline form of carbon.
Reason :
Carbon atoms in diamond are tetrahedral in nature.
(A) Both reason and assertion are correct and reason is the correct explanation for the assertion.
(B) both reason and assertion are correct. But the reason is not the correct explanation for the assertion.
(C) Assertion is correct but the reason is wrong.
(D) Both assertion and reason are wrong.

Answer 1

Diamond is an allotrope of carbon, like diamond there are other allotropes of carbon. The way in which the carbon atoms are bonded in the crystal structure, will determine the hardness of the element

Complete Solution :
- Diamond is the element which is found in the earth’s mantle under very high temperature and pressure. It is one of the hardest elements found in the world. Diamond is the allotrope of carbon. Arrangement of the carbon atom in the diamond is isometric. Isometric means arrangement in a regular pattern.
- Carbon atoms have an electronic configuration of $1{s^2}2{s^2}2{p^2}$. It has 4 valence electrons. All these electrons are bonded to other four carbon atoms. This bonding is very strong and cannot be separated. The type of bond present in carbon atoms is covalent. Since it is bonded to four other carbon atoms, diamond will be having a hybridisation of $s{p^3}$. Thus, forming a tetrahedral structure. Since all the electrons in the diamond are completely filled it is an insulator of heat.
- Diamond will be forming an infinite three-dimensional network on bonding with other carbon atoms. This is the main reason for its hardness.
Therefore, Both Assertion and reason are correct, but reason is not the correct explanation for the assertion.
So, the correct answer is “Option B”.

Additional Information:
Comparison of diamond and graphite:

Diamond	Graphite
Diamond is very hard and colourless	Graphite is very soft, slippery and black in colour.
Diamond is an insulator.	Graphite is a good conductor of electricity.
Diamonds have $s{p^3}$ hybridisation.	Graphite has $s{p^2}$ hybridisation.
They have tetrahedral structure.	They have planar structure.

Note: Along with diamond, carbon also has other allotropes. But all the allotropes will not have the same physical and chemical property. The only thing which will be common in them is the element carbon.