An indicator is a substance that changes its color in acidic and basic medium. An indicator shows one color in an acidic medium and different colors in a basic medium so that they are called indicators. There are different types of indicators:
- Indicators derived from natural sources are called natural indicators. eg:- Litmus, red cabbage
- indicators prepared in the laboratory are called synthetic indicators. eg:- Phenophtaline
- Olfactory indicators are which give different odors in acidic and basic medium. eg:-Onion, vanilla essence, etc.