What chemical color change is observed when phenolphthalein indicator is added to an aqueous sodium hydroxide solution?
Answer and explanation
Correct answer: D. Turns bright pink above pH 8.2
Phenolphthalein is colorless in acidic and neutral solutions (pH < 8.2) and turns bright pink/magenta in basic solutions (pH 8.2 - 10.0) due to deprotonation and formation of a quinoid conjugated chromophore system.
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