Why does dry HCl gas not change the colour of dry litmus paper

Why does dry HCl gas not change the colour of dry litmus paper

Answer: Dry HCl gas does not form H⁺ions. It does not show its acidic character. When in the aqueous solution, an acid ionizes to form H⁺ions. In this case, neither HCl is in an aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change.