When the pH of a solution is decreased from 10 to 5, which pH indicator changes from a colored to a colorless solution?

Phenolphthalein is the correct choice because it is specifically known for its behavior in different pH environments. In alkaline solutions (pH above 8.2), phenolphthalein exhibits a pink color, indicating a basic environment. As the pH decreases and moves towards acidic conditions (pH 5), phenolphthalein transitions to a colorless form, which occurs in acidic solutions. The significant change from a colored to a colorless solution when moving from pH 10 to pH 5 highlights its functionality as a pH indicator.

Other indicators have different ranges and behaviors. Litmus does not undergo such a stark color change between these specific pH levels, as it only shifts colors around pH 7. Methyl orange changes color in more acidic conditions, specifically around pH 3.1 to 4.4, which does not apply here. Bromothymol blue transitions between yellow and blue around neutral pH levels (6.0-7.6) and would not display the same noticeable color shift from a colored to a colorless state. Therefore, phenolphthalein’s distinct shift from pink to colorless makes it the accurate choice in this scenario.