Suppose you are given an unknown solution and you need to test its pH. The pH meter is broken, and all you have is the indicator bromothymol blue to use. You add two drops of bromothymol blue to 10 mL of your unknown, and the solution turns a bright yellow. Which of the following is the best estimate of the pH of the unknown solution? B. 8.5 C. 15 D. 7.0

none of those options are correct, if the solution turns bright yellow then it indicates an acidic solution, with a pH that would go around 5 or 6 approximately.

Explanation:

Bromothymol blue is a pH indicator that acts as a weak acid in solution, this means that it can be easily protonated or deprotonated, appearing yellow or blue, respectively. In a neutral solution (ph = 7) it usually reflects a green-blue color.

The protonated form of bromothymol blue has its peak of absorbtion at 692nm, reflecting then the yellow light in acidic solutions.