Question

why is hcl gas is unable to change the colour of a dry blue litmus paper?what happens if the litmus paper is moistened?

Answer 1

The litmus paper will only reacted in moistened form and HCL will also oy react when it comes when the contact of wet litmus paper .
therefore when the litmus paper is moistened the gas comes in contact with it and get reacted

Answer 2

hcl gas does not dissociate H+ ions to change the colour of the litmus paper..when litmus paper is moistened H+ ions are dissociated to change the colour of the litmus paper..