Question

An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change?

Options

• Sodium hydroxide

• Hydrochloric acid

• Baking soda

• Slaked lime

Answer 1

Hydrochloric acid

Explanation:

When an aqueous solution turns red litmus blue, it indicates the solution is basic (alkaline). Red litmus paper turns blue in the presence of a base. To reverse this change, we need to add an acid to neutralise the base and turn the solution acidic or neutral. Hydrochloric acid neutralises the base and reverses the change.