Which indicator turns red in acidic solutions and blue in basic solutions?

The indicator that turns red in acidic solutions and blue in basic solutions is litmus. Litmus is a classic acid-base indicator derived from lichens. This indicator changes color depending on the pH of the solution: it is red in acidic conditions (pH below 7) and blue in basic or alkaline conditions (pH above 7).

Litmus is often used in laboratories and educational settings due to its simplicity and clear color change, making it easy to identify the nature of a solution. Other indicators also exhibit color changes with pH, but they display different color transitions. For instance, universal indicator can show a range of colors depending on the pH value, while phenolphthalein is colorless in acidic solutions and turns pink in basic solutions. Bromothymol blue changes from yellow in acidic conditions to blue in basic conditions but does not match the specific color change of red to blue exhibited by litmus.