Question

Which of the following conducts electricity?
(A) Crystalline NaCl
(B) Fused NaCl
(C) Molten sulphur
(D) Diamond

Answer 1

Hint: A substance conducts electricity when there are free electrons in its lattice. Fused salt stands for its liquid state which is obtained at higher temperatures. Crystalline state is a solid state of a salt where arrangement of the ions is regular.


Complete step by step answer:
Let us first understand how metal conducts electricity.
- Electric conductors can conduct electrical current very easily because of their free electrons. Substance that has charged particles like electrons and ions, which are free to move, can conduct electricity.
- Most of the metals are considered to be good conductors of electrical current. Copper is one of the more popular materials that are used as conductors.
Now considering the question,
- The fused NaCl (sodium chloride) contains mobile Sodium and Chloride ions obtained by breaking the lattice by heat & thus it is a good conductor of electricity.
- In contrast, crystalline NaCl contains a closely packed lattice of alternate Sodium and Chloride ions each having a coordination no of 6 i.e. each cation is surrounded by 6 anions & vice versa. Thus there are no free charge carriers; hence it is a non conductor of electricity.
- Ionic compounds conduct electricity when they undergo a phase transition from solid to liquid.
- Diamond is a bad conductor of electricity due to its tightly packed tetrahedral geometry. As Sulphur is a non-metal, it’s a poor conductor.


Therefore, fused NaCl conducts electricity because of their free electrons. Hence, option B is the required answer.


Note: Remember that fused and molten states are synonyms of each other. However in case of molten sulphur, it will not be able to conduct electricity as the non-metals do not have free electrons in their structure that can conduct electricity.