In the dark waters just below the photic zone, because of cellular respiration, the concentration of dissolved carbon dioxide is higher relative to dissolved oxygen. In cellular respiration living organisms use oxygen and release carbon dioxide, because there is little or no light there is no photosynthesis and oxygen is little produced.
I think there is a lack of information in the given problem above such as the grams of copper sulfate and sodium hydroxide that was used in the experiment. Kindly resubmit the question with the complete details so that we can help you. Thank you.
