What was the purpose of the starch test tube containing only water Explain.?

The starch test tube containing only water serves as a control to establish a baseline for the experiment. By including this test tube, researchers can confirm that any changes observed in the other test tubes are due to the presence of starch and not other variables. It helps ensure that the experimental results are valid and reliable by demonstrating that water alone does not produce any reaction or color change in the starch test.