A universal indicator is a pH indicator that changes color to show the acidity or alkalinity of a solution. It is a mixture of several different indicators, allowing it to provide a wide range of colors corresponding to different pH levels, typically from 0 to 14. This makes it useful in various scientific applications, including chemistry and biology. When a universal indicator is added to a solution, it reacts with the hydrogen ions present. For example, in acidic solutions, it may turn red, while in alkaline solutions, it may shift to blue or purple. This visual representation helps scientists and students easily determine the pH level of a substance.