Answer:

The best indicator for the detection of the end point in the titration of a weak acid and a strong base is phenolphthalein (option D). Phenolphthalein is a commonly used indicator in acid-base titrations due to its ability to change color within a specific pH range.

Explanation:

1. Acid-Base Titration:
In an acid-base titration, a solution of known concentration (the titrant) is added to a solution of unknown concentration (the analyte) until the reaction between the two is complete. The point at which the reaction is complete is called the end point.

2. Indicators:
Indicators are substances that change color depending on the pH of the solution. They are used to determine the end point of a titration by visually indicating the completion of the reaction. Different indicators have different pH ranges in which they change color, making them suitable for different types of titrations.

3. Weak Acid and Strong Base Titration:
In the titration of a weak acid and a strong base, the pH of the solution changes gradually as the titrant is added. Initially, the solution is acidic due to the presence of the weak acid. As the strong base is added, it reacts with the weak acid to form a salt and water. The pH of the solution gradually increases as the acid is neutralized.

4. Phenolphthalein:
Phenolphthalein is a suitable indicator for the titration of a weak acid and a strong base because its color change occurs in the pH range of 8 to 9.6. This pH range is appropriate for this type of titration because it corresponds to the region where the weak acid has been mostly neutralized, and the solution is becoming basic.

5. Color Change:
Phenolphthalein is colorless in acidic solutions (pH < 8)="" and="" turns="" pink="" or="" magenta="" in="" basic="" solutions="" (ph="" /> 9.6). Therefore, during the titration, as the strong base is added and the pH of the solution increases, the phenolphthalein gradually changes from colorless to pink, indicating the end point of the reaction.

Conclusion:
In conclusion, phenolphthalein is the best indicator for the detection of the end point in the titration of a weak acid and a strong base because its color change occurs within the appropriate pH range for this type of titration.