Indicators
An indicator is a substance that changes color in response to a change in the conditions of its solution. It is used to determine the acidity or alkalinity of a solution. Indicators are often used in titrations to determine the endpoint of the reaction.

Common Indicators
1. Litmus: Litmus is a commonly used indicator that turns red in acidic solutions and blue in alkaline solutions. It is available in the form of blue litmus paper and red litmus paper.
2. Phenolphthalein: Phenolphthalein is another commonly used indicator that is colorless in acidic solutions and pink in alkaline solutions. It is often used in titrations to determine the endpoint of the reaction.
3. Methyl orange: Methyl orange is an indicator that is red in acidic solutions and yellow in alkaline solutions. It is often used in titrations of strong acids and strong bases.
4. Bromothymol blue: Bromothymol blue is a pH indicator that is yellow in acidic solutions, green in neutral solutions, and blue in alkaline solutions. It is often used in biology labs to demonstrate the process of photosynthesis.
Using indicators can help determine the pH of a solution and whether it is acidic or alkaline. Different indicators are used based on the pH range being tested and the color change that is desired.

Solutions of substances that show different colour in acidic basic and neutral solutions are called indicators