Phenolphthalein changes color from colorless to which color?

• A. Red
• B. Blue
• C. Yellow
• D. Pink

Answer: (D)

Phenolphthalein is an acid–base indicator that changes color with pH. In acidic solutions it stays colorless, but as the solution becomes basic and the pH rises past about 8.2, the molecule loses a proton and shifts to a colored form. That deprotonated form gives a pink (rose/magenta) color, so the color change from colorless to pink signals the endpoint in a titration. It doesn’t turn red, blue, or yellow under typical conditions for this indicator.