Answer: A.Placing different groups of people in different colored rooms and recording their mood
Explanation:
An observational study is a study in which a researcher just records behavior in a particular manner without interfering with the behavior.
In this study, the researcher has no influence or control over the variables .
From the given options , only option A representing a situation which can be an example of observational study."Placing different groups of people in different colored rooms and recording their mood "
Here the researcher just recording the mood of people without any influence.