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
Correct answer: (1) HCI solution
Explanation: Phenolphthalein is a universal indicator that is colourless in an acidic and neutral environment but shows pink colour in a basic environment.
As the solution shows a pink colour, it should be basic in nature. Therefore, to obtain a colourless solution again, the student needs to add an excess of the acidic solution in it. Hence, the correct answer is the HCl solution.
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