1. Litmus: Litmus is a natural dye extracted from lichens. It is available in two forms: red litmus and blue litmus. Red litmus turns blue in basic solutions, while blue litmus turns red in acidic solutions.
2. Phenolphthalein: Phenolphthalein is a synthetic indicator that is colourless in acidic solutions and turns pink in basic solutions.
3. Methyl orange: Methyl orange is another synthetic indicator that is red in acidic solutions and turns yellow in basic solutions.
4. Bromothymol blue: Bromothymol blue is a synthetic indicator that is yellow in acidic solutions, turns green in neutral solutions, and becomes blue in basic solutions.
5. Universal indicator: Universal indicator is a mixture of several indicators that produces a wide range of colours depending on the pH of the solution. It is often used to estimate the pH of a solution quickly and easily.
These are just a few examples of the many substances that can be used as indicators in various applications. The choice of indicator depends on the specific requirements of the experiment or application.
