Which indicator is used in the method?

• A. Phenolphthalein
• B. Bromothymol Blue
• C. Methyl Orange
• D. Phenol Red

Answer: (A)

Choosing an indicator hinges on matching its color-change range to the pH at the titration’s equivalence point. In this method, the endpoint lies in the basic region, so you want an indicator that stays colorless in acid and turns pink in base around pH 8.2–10.0. Phenolphthalein fits perfectly: it is colorless in acidic solutions and develops a vivid pink as the solution becomes basic, providing a clear and sharp end point for a weak acid–strong base titration. Other indicators shift colors outside this basic window or provide less distinct changes in this titration condition, making them less reliable for this method.