Ionic compounds can conduct electricity when dissolved in water or melted, because a. they have shared electrons. b. they have no ions to contribute to the solution. c. the ions are fixed in place. d. the ions are free to move.

So,

Ionic compounds are compounds composed of ions.  The following are soluble ionic compounds (they dissolve in water):

NaCl(s) --> Na⁺(aq) + Cl⁻(aq)
NaOH(s) --> Na⁺(aq) + OH⁻(aq)

The following are insoluble ionic compounds (they have low solubilities):

Al₂O₃ --> 2Al³⁺+3O²⁻
AgCl --> Ag⁺ + Cl⁻

These compounds can only be appreciably separated by melting or by dissolving them in enormous amounts of water (the concentration will still be very low).

Ionic compounds have electrons that are locked in place because of the strong ionic attractions between the ions.  A charge is produced by moving electrons.  Since the ions in melted ionic compounds are free to move, their electrons are no longer locked, allowing the ionic liquid to conduct electricity.

NaCl(s) --> Na⁺(l) + Cl⁻(l)

The answer is D.

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