Question

Which of the following can conduct electricity in solid state?
(A) Sucrose, ${{C}_{12}}{{H}_{22}}{{O}_{11}}(s)$
(B) Graphite, C(s)
(C) Sodium hydroxide, NaOH (s)
(C) Iron (III) chloride, $FeC{{l}_{3}}\left( s \right)$
(D) Iodine, ${{I}_{2}}(s)$

Answer 1

Hint:: To conduct electricity, one substance must contain a delocalised, unpaired electron. To answer this question, check closely the structures of the compounds and see if they have any charged particles.
complete step by step answer:
To solve this question, let us discuss each option one by one.
Firstly we have sucrose. In sucrose, all the atoms are bonded to each other through strong covalent bonds. There is no charged particle present in it to conduct electricity neither in solid state nor in liquid state.
Then we have graphite. Graphite is a crystalline allotrope of carbon and it has a slippery surface. In graphite, the carbon atoms are arranged in a hexagonal structure and each carbon atom is attached to three other carbon atoms.
We know that carbon has four valence electrons in its outermost shell. In graphite each carbon is bonded to three other carbon atoms hence leaving behind a free electron. Due to the presence of this one delocalised electron, graphite is a good conductor of electricity.
Next we have sodium hydroxide. It is an ionic compound i.e. the atoms are bonded through ionic bonds. In an aqueous solution, the bond breaks and it dissociates into $N{{a}^{+}}\text{ and O}{{\text{H}}^{-}}$. Movement of electric current is possible due to the presence of these ions in the solution. However, in a solid state the bond is intact and therefore it cannot conduct electricity.
Then we have iron (III) chloride. Iron conducts electricity in solid state but iron (III) chloride is an ionic compound and these compounds do not conduct electricity in solid state.
And lastly we have iodine. Iodine is a non-metal and it exists as a dimer. It has no charged species in it so it does not conduct electricity.
Therefore, the correct answer is option (B) Graphite, C(s).

Note: Graphite and diamond both are allotropes of carbon however diamond does not conduct electricity as graphite. This is due to the fact that in diamond all the electrons in the valence shell of carbon are engaged to form a covalent bond with four other carbon atoms. Thus, there is no free electron in diamond like graphite.