The correct answer is B: Drastic changes with carbon dioxide increasing and oxygen decreasing.
Elodea is a type of aquatic plant that performs photosynthesis, which is the process by which plants use sunlight, water, and carbon dioxide to produce oxygen and glucose. During photosynthesis, the plant absorbs carbon dioxide from the air and releases oxygen.
Snails, on the other hand, breathe using a process called respiration, which is the opposite of photosynthesis. During respiration, the snail takes in oxygen and releases carbon dioxide.
When you put a sprig of Elodea and a snail in a test tube with the lights on, the Elodea will perform photosynthesis and the snail will perform respiration. As a result, the carbon dioxide levels in the test tube will increase and the oxygen levels will decrease. The changes may be drastic, depending on the size of the test tube, the amount of Elodea and snail, and the intensity of the light.