To reverse the change of an aqueous solution that turns red litmus blue, you would add hydrochloric acid.
Here’s why:
– The solution that turns red litmus blue is basic (alkaline).
– Ammonium hydroxide is also a base, which would not reverse the change.
– Hydrochloric acid is an acid, which can neutralize the base and turn the solution acidic again, causing the litmus paper to turn red once more.