Question

Which of the following is an insulator?
(A) Wood
(B) Iron
(C) Carbon
(D) Silver

Answer 1

Hint: In order to conduct electricity, a substance should contain ‘sea of electrons’ which are mobile. Think about what an insulator is. Take a look at the given options and think which one has the property of conductance of electricity.

Complete Answer:
Insulators are the materials which do not conduct electricity. These substances have a large gap between the conduction band and valence band and thus, electrons are not able to jump from conduction band to valence band. Conductors are the substances which have the potential to conduct electricity. These substances have a very small gap between the conduction band and valence band and thus, electrons can easily jump from conduction band to valence band and conduct electricity.
Metals are very good conductors of electricity. In order to conduct electricity, a substance should contain a ‘sea of electrons’. Since both iron and silver are metals, so they are conductors of electricity.
The form of carbon that is a good conductor of electricity is Graphite. Graphite is an allotrope of carbon that has the properties of both metal and non-metal. The reason why graphite is a good conductor of electricity is because of the mobility of the electrons in its outer valence shell. Carbon, however, is an insulator in diamond form. So, wood is an insulator.
Hence, the correct answer is Option A.

Note:
Generally, non-metals are not conductors of electricity that is, they are insulators. But graphite, an allotrope of carbon is an exception, it is a very good conductor of electricity. The electrical wires are made up of copper and are insulated with rubber or plastic because they are bad conductors of electricity and do not conduct electricity and thus, ensure safety from electrical shock.