Philippe did an experiment in science class in which he was trying to determine what is happening to carbon dioxide in various situations. He set up his lab using aquatic snails and Elodea aquatic plants. He put four tubes in a light environment and four tubes in a dark environment. He used a solution called bromothymol blue to indicate the presence of carbon dioxide in the water.
When bromothymol blue is placed in water it will be green. As carbon dioxide is added to water, the solution will turn yellow. When you remove carbon dioxide from the solution, it will turn blue.

What color would each test tube become after 24 hours?