Question

Why does an aqueous solution of an acid conduct electricity ?? Why does dry hcl gas not change the colour of dry litmus paper ?

Answer 1

the colour of litmus paper changes only in the presence of ions like hydrogen or hydronium.but hcl can produce these ions only in the form of aqeous solution.hence colur does not change

Answer 2

In aqueous solution acid furnishes into h ions and ions are the carrier of electricity.
Dry hcl gas does not change the colour of dry litmus paper because ions are not formed in dry litmus solution.