Final answer:
In the experiment comparing the boiling points of water and milk, the independent variable is the type of liquid, while the dependent variable is the temperature at which boiling occurs. Controlled variables include the amount of liquid, atmospheric pressure, and the heat source, ensuring a fair comparison.
Step-by-step explanation:
Experiment Variables and Constants
An experiment is a scientific procedure undertaken to make a discovery, test a hypothesis, or demonstrate a known fact. In an experiment to determine whether water or milk will boil first, the independent variable is the type of liquid being heated (water or milk), because it is what the experimenter changes to observe the effect on the dependent variable.
The dependent variable is the temperature at which boiling occurs, since it depends on the independent variable. Factors that must remain constant to ensure a fair test, also known as controlled variables, include the volume of the liquids, the atmospheric pressure, and the source of heat.
Water has a boiling point of 100°C under standard atmospheric pressure. Upon reaching its boiling point, water undergoes a phase change from liquid to gas (vapor). This distinction in boiling points between water and milk will ultimately determine which substance boils first in the experiment.