you and your friend are walking along a beach in Maine on January 15, at 8 am. you notice a thermometer on a nearby building that reads -1 c. you also notice that there is snow on the roof of the building and icicles hanging from the room. you further notice a pool of sea water in the sand near the ocean. your friend looks at the icicles and pool and says, "How come the water on the if frozen and the sea water is not?" you answer, "I think that the salt in the sea water keeps it from freezing at -1c." your friend asks, "How can you be sure?" you answer, "im going to get some fresh water and some salt water and expose them to a temperature of -1c and see what happens."

What is the independent variable?
What is the control group?

you are testing the effect of salt on water freezing or not. freshwater does not have salt, so it will be the control since you know it will freeze. salt water has salt, and since that is what you are testing, your salt water is your independent variable.

do not confuse your independent variable with your dependent variable!