Question

why doesn't solid sodium chloride(common salt )conduct electricity

Answer 1

Sodium chloride does not conduct electricity in solid state, However when sodium chloride is present in molten form, it conducts electricity.

The essential requirement for conducting electricity is presence of free electrons or free ions.

Since in Solid state, sodium and chloride ions are held together with strong strong electrostatic force of attraction therefore they are unable to move and thus they act as a bad conductor of electricity in solid state. Whereas, sodium chloride dissociates into ions in molten state or aqueous solutions. Hence they conduct electricity well.