Consider the uninoculated sim tube. is it a positive or a negative control in each test

It is a negative control. It minimizes concern about false positive results. No ingredients within the medium which can produce a positive effect at any stage of testing. It shows the original colour changes. Experiemental may not be apparent without comparison to the original.

Negative control.

Explanation:

SIM (sulfur indole motility)experiment is used to identify microorganisms having ability to produce indole, reduce sulfur, and to show motility. In each scientific experiment, a negative control is also used to compare actual test results as negative control does not show any response.

In this experiment, the uninoculated tube with SIM medium will be  considered as negative control as it doe not any microorganism, thus, no response is expected from this tube.

Thus, the correct answer is 'negative control.'

the contamination

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