Answer:Phenolphthalein is a chemical compound and plays the role of a acid-base indicator. When used as an indicator with a solution with pH, phenolphthalein is colourless below pH 8.5 and attains a pink to deep red hue above pH 9.0.
Using Phenolphthalein with phosphoric acid of pH ~3 will yield a colourless solution. Orange IV however seems fit as it would be a better indicator because it changes color around a pH of 2-3.
Step-by-step explanation: