Question

Which of the following is an insulator?
A.Graphite
B.Silicon
C.Diamond
D.Aluminium

Answer 1

Hint: Insulators are those materials that obstruct the free flow of electrons, hence, do not conduct electricity through them, whereas conductor in contrast permits the free flow of electrons, hence, they conduct electricity.

Complete step by step answer:

Graphite – Graphite is made up of carbon atoms. Each carbon atom is bonded to three other carbon atoms. This structure leaves one electron to become delocalized, and this delocalized electron is free to conduct electricity. So, graphite is a conductor. Hence, option (a) is incorrect.
Silicon – Silicon with atomic number 14 is neither a metal nor a non-metal. It is a metalloid which has both properties of metal, and nonmetals. That’s why, it is a semiconductor which means that it can conduct electricity. So, silicon does not come under the category of insulators. Hence, option (b) is incorrect.
Diamond – Diamond structure is made up of carbon. Each carbon in its structure is covalently bonded with other four carbon atoms, giving it a tetrahedral geometry. This arrangement leads to delocalization of electrons, and so, it does not have any free electron to conduct electricity. Thus, diamond is an insulator. Hence, option (c) is correct.
Aluminium – Aluminium is a metal, and has metallic bonds between different atoms. Due to the formation of these metallic bonds, the valence electrons get detached, and move freely in the lattice. This free electron can conduct electricity. Thus, aluminium is a conductor. Hence, option (d) is incorrect.

Which shows the option C is the correct answer.

Note:
Diamond does not conduct electricity but it is a very good thermal conductor. Diamond has tetravalent arrangement of covalently bonded atoms. These bonds are very stiff bonds between light carbon atoms, which give it high thermal conductivity.