The ph indicator bromothymol blue turns yellow when co2 gas is added to a solution and blue when co2 is removed from a solution. which statement is a hypothesis you could test using a solution with bromothymol blue? a. if yeast cells give off o2, then the solution will turn from yellow to blue. b. if fish give off heat, then the solution will turn from blue to yellow. c. if water plants take in co2, then the solution will turn from yellow to blue. d. if algae give off o2, then the solution will turn from blue to yellow.