Final answer:
The negative control tube that does not show any change indicates the amylase solution was not contaminated with maltose, ensuring that maltose detected in other tubes is the result of amylase activity on starch.
Step-by-step explanation:
The tube indicating that the amylase solution was not contaminated with maltose is the one that shows no change in color or presence of maltose in an experiment designed to test enzyme activity. In an experiment where amylase catalyzes the breakdown of starch into maltose, any production of maltose in the absence of starch suggests contamination.
Therefore, a negative control would typically contain the amylase solution without any starch substrate to confirm that the enzyme preparation is free of maltose. If there is no change in the negative control, it implies that the amylase solution is uncontaminated and any subsequent color change due to the presence of maltose in the experimental tubes can be attributed to the enzymatic activity of amylase on the starch substrate.