Phenolphthalein, (C 20 H 14 O 4), an organic compound of the phthalein family that is widely employed as an acid-base indicator. As an indicator of a solution's pH, phenolphthalein is colour less below pH 8.5 and attains a pink to deep red hue above pH 9.0. Correct option is A) In alkaline solution, phenolphthalein gives pink color as it works as an indicator which shows its endpoint when it reacts with hydroxide ions of the base. It is a commonly used indicator in acid-base titrations. In acidic solution when acid is added, phenolphthalein gives a colorless solution. · At first end point, phenolphthalein colour change is observed and it corresponds to reaction HCl with NaOH (to . because phenolpthalein changes its colour between pH 8.1-10, and for titration of strong acid and weak base pH is slightly less than 7, so it does not show any change in colour, hence it is not suitable indicator for strong acid - weak.