Answer: (d) Hydrochloric acid
If the solution turns red litmus to blue colour then the solution should be basic in nature. Its effect can be neutralized by adding an acid.
What is Neutralization?
It is an acid-base reaction in which an acid reacts with a base to form salt and water. The pH of the neutralized solution depends upon the acid strength of the reactants and their concentrations. The neutralization reaction is best represented as:
Acid + Base → Salt + Water