* Lack of Free Charge Carriers: Hydrogen chloride gas exists as individual molecules, with a covalent bond between the hydrogen and chlorine atoms. This means there are no free electrons or ions readily available to carry an electrical current.

* Non-Polar Nature: HCl is a polar molecule, but in the gaseous state, the molecules are far apart and their polarity doesn't lead to significant charge separation. This prevents the formation of an electrical current.

However, things change when hydrogen chloride dissolves in water:

* Formation of Ions: HCl readily dissolves in water, and the reaction produces hydronium ions (H3O+) and chloride ions (Cl-). These ions are free to move and can conduct electricity.

* Strong Electrolyte: The high concentration of ions in an aqueous solution of HCl makes it a strong electrolyte, meaning it conducts electricity very well.

In Summary:

* Gaseous HCl: Not a good conductor of electricity.

* Aqueous HCl: A strong conductor of electricity.