Answer:
A vaccum should be used for the control group chamber.
Step-by-step explanation:
In an experiment, a control is an experiment or observation designed to minimize the effects of variables other than the independent variable. The introduction of a control increases the reliability of the results; often through a comparison between the control measurements and the other measurements.
A vaccum according to this experiment is a chamber that will have no pressure within it. This will give a benchmark of the effect of pressure in this experiment.