Why can a solution of copper sulphate conduct electricity but solid copper sulphate cannot?

For conduction of electricity to occur, charged particles such as ions must be free to move so that electrical current can flow. In a solution of copper sulphate, the copper ions and sulphate ions are dissociated and are free to move. In solid copper sulphate the copper and sulphate ions are held rigidly in a giant ionic lattice by strong ionic bonds and cannot move.