Answer:
The correct option is "The rate of photosynthesis decreased in the dark, thus the elodea used less CO2. The elodea and snails continued to produce CO2 through cellular respiration, raising the level of CO2 in the tube, causing the solution to become more acidic (yellow)."
Step-by-step explanation:
The process of photosynthesis is dependent on light energy. As the test- tubes were kept in the dark hence, the rate of photosynthesis was minimal. Less carbon dioxide was used for this process by the elodea.
The process of cellular respiration is not dependent on light. Hence, both the snail and elodea will carry out respiration and release carbon dioxide. Due to this carbon dioxide, the solution will turn acidic.