Question

Which experimental setup represented the negative control group? The one where we didn't expect a cloud to form.
Glass with only hot water
Glass with hot water and smoke particles
Glass with cold water and smoke particles
Glass with only cold water

Answer 1

In an experimental setup involving cloud formation, the negative control group is the one where no cloud is expected to form. In your examples, the glass with only cold water would be the negative control group, as it typically would not produce a cloud compared to the other setups that involve hot water or smoke particles, which are more likely to facilitate cloud formation.