Question

A student was asked to test an unknown colourless solution with an indicator. When he added a few drops of phenophthalein indicator, the solution turned pink. Which one of the following chemicals should be added in excess so as to obtain the colourless solution again?
(1) HCI solution
(2) NaOH solution
(3) NH₃ solution
(4) NaCI solution

Answer 1

Phenolphthalein is a universal indicator, it is colorless in an acidic and neutral environment but shows pink color in a basic environment.
As it shows a pink color, the solution is basic. Therefore, to obtain a colorless solution again, the student needs to add an excess of the acidic solution in it. So, out of all the given options, only the HCl solution is suitable.

Hence, the correct answer is option 1.