Question

Dry HCl gas does not turn blue to red litmus whereas dilute HCl does

Answer 1

Dry HCL gas does not turn blue to red lithmus because dry HCL does not free ions to change the color of lithmus paper whereas dilute HCL have a little amount of water dissolved which free the ions H+ ions and change the color of lithmus paper

Answer 2

Heya !!!

This is your answer.....

We know that acids show their acidic behaviour when the H+ ions ionize.
H+ ions ionize only when mixed with water.....

So... when HCL is dry. The H+ ions do not ionize and hence they do not show their acidic behaviour.

Hope it helps