In order to study the neutralisation reaction of acid and base, a student took 10 mL of dilute hydrochloric acid in a conical flask and added a few drops of phenolphthalein indicator to it. He then added dilute sodium hydroxide solution to the conical flask dropwise with a dropper while shaking the conical flask constantly. When the acid is completely neutralised by the base, the solution in conical flask will turn :
(1) slightly red
(2) slightly yellow
(3) colourless
(4) slightly pink

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Solution

Phenolphthalein is a colourless indicator in acid and in neutral solutions but in basic solutions, it shows pink color. So, when dilute sodium hydroxide is added until the acid is completely neutralized, the solution becomes colourless.

Hence, the correct answer is option 4.

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Phenolphthalein is a colourless indicator in acid and in neutral solutions but in basic solutions, it shows pink color. So, when dilute sodium hydroxide is added until the acid is completely neutralized, the solution becomes colourless. Hence, the correct answer is option 4.

Phenolphthalein is a colourless indicator in acid and in neutral solutions but in basic solutions, it shows pink color. So, when dilute sodium hydroxide is added until the acid is completely neutralized, the solution becomes colourless.

Hence, the correct answer is option 4.