Answer :
The answer is Option 4 , pink phenolphthalein .
What is an Indicator ?
A pH indicator or acid-base indicator is a compound that changes color in solution over a narrow range of pH values.
Only a small amount of indicator compound is needed to produce a visible color change.
Some of the indicators are methyl orange , litmus paper , phenolphthalein etc.
As the pH mentioned is 12 , it is a base
In basic medium phenolphthalein changes its colour to pink while red litmus paper turns blue .
Therefore The answer is Option 4 , pink phenolphthalein .
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