Answer:
The correct answer will be option-B.
Step-by-step explanation:
An experiment is performed to test the predicted and proposed hypothesis.
The experiment contains two types of group of samples: the experimental group on which the variable is to tested (independent variable) and the control group in which the independent variable is kept constant.
In the give question, the hypothesis is the popcorn which is kept in the refrigerator pops better so the independent variable will be cold temperature. So the experimental group will be the samples which are kept in cold temperature or refrigerator as the cold temperature is provided in these samples.
Thus, Option-B is the correct answer.