Answer. Indicator is the organic compounds. It has different colors in acidic and alkaline solutions. Litmus is a common indicator. It is red in j acidic solution and blue in alkaline solution.
Each indicator has a specific .colour in acidic medium which changes to another colour in basic medium. For example, phenolphthalein is colorless in strongly acidic solution and red in strongly alkaline solution. It changes colour at a pH of about 9: This means phenolphthalein is colorless in a solution if pH less than 9. If the pH is above 9, phenolphthalein is red.