Ions contained in a crystalline (solid) substance, located in the nodes of the crystal lattice, are connected to each other and cannot move, therefore solid electrolytes do not conduct electric current. Sodium chloride, when dissolved in water, decomposes into ions (positively and negatively charged), which are able to move freely, and are charge carriers. Under the influence of an electric field, the movement of ions becomes directional (an electric current arises).
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