In an experimental investigation, the variable that the researcher changes or manipulates in order to see its effects is called

Test group is a group that is modified or changed by the researcher and is then compared to the experimental group while carrying out an experiment.

Explanation:

While observing the data of the test group, it has to be compared with the control group to see if there is any effect of the treatment on the test or not. The control can be positive or negative or both to which the test group is compared.

not always but somethings can be reproduced in a laboratory.

density and pressure