Solid sodium chloride does not conduct electricity, but molten sodium chloride does, because
Correct answer: B. the ions become free to move only when the lattice breaks down
- A. melting converts the ions into atoms
- B. the ions become free to move only when the lattice breaks down
- C. electrons are released on melting
- D. the molten salt contains water
Explanation
Conduction in an ionic compound needs mobile charge carriers, and in the solid the ions are locked in fixed lattice positions even though they are charged. Melting frees them to migrate towards the electrodes, and dissolving in water has the same effect. No electrons are released and the ions remain ions throughout, which rules out the other explanations.
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About Ionic and Molecular Crystals
Ionic crystals contain oppositely charged ions held by electrostatic forces, whereas molecular crystals contain discrete molecules joined by weaker intermolecular forces. Their structures explain differences in melting point, hardness, volatility, solubility and electrical conductivity, especially between solid and molten states.
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