What is the substance that changes color to red in acid and yellow in a base?

Methyl orange is a pH indicator that undergoes a distinct color change depending on the acidity or basicity of the solution it is in. It appears red in acidic conditions (when the pH is below 3.1) and changes to yellow when the solution is neutral or basic (above pH 4.4). This property makes methyl orange particularly useful in titrations involving strong acids and weak bases, as its color change is clear and occurs within a pH range that effectively highlights the transition from acid to base.

In contrast, other indicators such as phenolphthalein and bromothymol blue display different color changes in their corresponding pH ranges. Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions, while bromothymol blue transitions from yellow in acidic conditions to blue in basic conditions. Litmus is also a pH indicator but changes from red in acid to blue in a base, which does not match the specific color transitions that methyl orange demonstrates.