Two test tubes are filled with a solution of bromthymol blue. a student exhales through a straw into each tube, and the bromthymol blue turns yellow. an aquatic green plant is placed in each tube, and the tubes are corked. one tube is placed in the dark, and the other tube is placed in direct sunlight. the yellow solution in the tube in sunlight turns blue, while the one in the dark remains yellow. which statement best explains why the solution in the tube placed in sunlight returns to a blue color? a) carbon dioxide was produced by respiration. b) carbon dioxide was removed by photosynthesis. c) oxygen was produced by photosynthesis. d) oxygen was removed by respiration.

Option B

Explanation:

When Bromthymol blue (BTB) receives carbon dioxide (after a student exhales into it), turns yellow. This yellow color is due to the formation of slightly acidic carbonic acid. Now,  an aquatic green plant is placed in both the test tubes and one of these test tube is placed in sunlight. Thus, the test tube kept in sun has all ideal requirements  that would allow the plant to photosynthesize. Photosynthesis process removes carbon dioxide from the test tube and hence it apperas blue again. While the test tube in dark still appears yellow in color

Hence, option B is correct

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