Question

Hydrogen chloride gas turns the blue litmus paper:

• A. green
• B. red
• C. black
• D. no change in colour

Answer 1

The correct option is D no change in colour

The colour of blue litmus paper changes only in the presence of ions like hydrogen ($H^{+}$) or hydronium ($H_3{O}^{+}$) ions. HCl can produce these ions only in an aqueous solution. Hence dry HCl gas does not change the colour of dry litmus paper.