Here's why:

* Detect or Measure: Indicators are used to signal the presence or amount of a specific substance. They often change color or other properties in the presence of the target substance.

* Convert into Another: Indicators can also be used to facilitate chemical reactions, acting as catalysts to convert one substance into another.

Examples of Indicators:

* pH indicators: Used to determine the acidity or alkalinity of a solution.

* Litmus paper: A classic example of a pH indicator that changes color in acidic or basic solutions.

* Starch indicator: Used to detect the presence of iodine, as it turns a dark blue-black color.

* Enzymes: Act as biological catalysts, facilitating specific chemical reactions in living organisms.

Let me know if you have more questions about indicators or other chemical processes!