Label each tube with your marker and place in the tube rack. Use the large pipette to put 5ml of deionized water into each tube. This will be the only time I will tell you what you will see. From now on, you will be on your own. Indeed, there are some instances when even I won't know what to expect.
Some labs are set up to work, others are more exploratory and open-ended.
However, in this case, you should have seen a significant darkening of the pigment in only the last tube, exactly where we expected it to be. The following will seem redundant and obvious to you, but you must assume that your reader has no prior knowledge of your work. Explain it well. Enzymatic activation of catechol by catechol oxidase in potato extract. The phenolic compound catechol, found in all plant cells, is converted to the dark pigment-product benzoquinone in the presence of the enzyme catechol oxidase and oxygen.