Question

(i) The conductivity of molten NaCl is due to movement of $N{a^ + }$ and $C{l^ - }$ ions.
(ii) Solid NaCl is also conductor of electricity
(iii) Molten sodium is a good conductor because of mobile electrons.
Which of the above statements are correct?
(A) All the statements are correct
(B) (ii) and (iii) are correct
(C) (i) and (iii) are correct
(D) Only (ii) is correct

Answer 1

The ionic compounds are good conductors of heat and electricity. NaCl is an ionic compound. Ionic compound is a chemical compound of ions held together by electrostatic forces of attractions which are termed as ionic bonding. The compound is neutral overall, but consists of positively charged ions called cation and negatively charged ions called anions.

Complete answer:

NaCl is an ionic compound which is formed by loss of one ${e^-}$ of Na and gaining one ${e^- }$ by chlorine. Ionic compounds have strong electrostatic forces of attraction. They are solid. In solid state they have no free electrons to move. Hence, they do not conduct the electricity in solid state, because in solid their ions are held in fixed position and cannot move. Hence the second statement is wrong.
In molten states they can conduct the electricity because their ions are free to move from place to place. In case NaCl has $N{a^ + }$ and $C{l^ - }$ ions when NaCl undergoes electrolysis, which involves conduction of electricity because of movement and discharge of the ions. Hence, the first and third statements are true.

So option (C) is the correct answer.

Note: Fused NaCl is the molten form of NaCl obtained by heating it at around ${800^0}\,C$. A salt in its fused state (liquid) state is able to conduct electricity same as when it is dissolved in water.