#2. Indophenol is used to indicate the presence of vitamin C in a substance by turning from blue to clear.

During an experiment, distilled water is dropped into Indophenol which then stays blue.

This test is an example of a negative control because we are using water to show what a negative reaction (no vitamin C is present) would look like.

Incidentally, we also do this test because if the blue solution turns clear, that indicates that our test tube or dropper is contaminated!

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