Final answer:
The control group serves to provide a baseline for measuring the effect of the independent variable and to compare the results with the experimental group, ensuring the study's validity.
Step-by-step explanation:
The purpose of the control group in an experiment is multi-faceted. One of its key purposes is to provide a baseline for measuring the effect of the independent variable. This ensures that any observed changes in the dependent variable can be attributed to the manipulation of the independent variable and not to other factors. Secondly, the control group helps to isolate the effect of the independent variable on the dependent variable by serving as a point of comparison. This comparison helps to validate the research by demonstrating that the changes observed in the experimental group are due to the experiment itself and not some other external factors.
Considering the options given in your question, the most accurate answer would be to compare the results of the experimental group with the control group (option 2) and to provide a baseline for measuring the effect of the independent variable (option 4). These options highlight the role of the control group in facilitating a comparison and providing a reference point in an experimental setup.