Question

Why does dry litmus paper changes it's colour in hydrochloric acid solution and not in dry hydrochloric acid gas when dipped

Answer 1

its because there is no breakdown of ions in dry Hcl gas but in aqueous solution there is a breakdown into H+ and Cl- and power of acid depends upon H+ ion concentration in aqueous solution so when there no actual breakdown of hcl gas into H+ and Cl- there is no change in colour of litmus paper

hope it helps

Answer 2

because hydrogen ions cannot exist alone but they exist after combining with water molecules