When phenolphthalein indicator is added to a colorless solution with a pH of 10, a student observes and concludes that the tested solution

1

remains colorless and is basic

2.

remains colorless and is acidic

3.

turns pink and is basic

4.

turns pink and is acidic

3. turns pink and is basic

Explanation:

Phenolphthalein is a pH indicator that remains colorless in acidic solutions, but in basic solutions it turns pink at a pH equal to 10.

Phenolphthalein is a weak acid that loses H + cations in solution. The phenolphthalein molecule is colorless, while the phenolphthalein-derived anion is pink. When a base is added, phenolphthalein loses H+, forming the anion and causing it to turn pink. The color change cannot be explained only on the basis of deprotonation, a structural change occurs with the appearance of a ketoenolic tautomerism.