In what state of matter do ions conduct electricity best?

Ions conduct electricity best in dissolved (aqueous) or molten form due to their ability to move freely. In these states, ionic compounds dissociate into their constituent ions, allowing them to move independently. This mobility of charged particles is essential for electrical conductivity because, as the ions migrate towards opposite electrodes, they carry an electric current.

In solid form, ionic compounds do not conduct electricity well because their ions are fixed in a crystalline lattice structure and cannot move freely. While in gaseous form, ions might be present, they are generally not in a sufficient concentration to conduct electricity effectively. The concept of supercooled forms typically refers to a liquid state that is below its normal freezing point without solidifying, and it does not inherently enhance ion mobility in a way that promotes conductivity. Therefore, the dissolved or molten state is optimal for ion movement and, consequently, for electrical conductivity.