Final answer:
In the context of the research question 'Does changing the volume of a gas affect the pressure?', the controlled variables would be temperature and the amount of the gas, which need to be held constant to accurately measure the effect of volume change on pressure.
Step-by-step explanation:
To address the research question, "Does changing the volume of a gas affect the pressure?", several variables need to be controlled during an experiment. When exploring the relationships among the pressure (P) of a gas and its volume (V), temperature (T), and amount (n), temperature and amount of the gas would typically be held constant to isolate the effect of changing volume on pressure.
This approach is consistent with the methodology used by early scientists to formulate various gas laws. These gas laws have shown that when the volume of a gas is decreased, the pressure increases if the temperature and the amount of gas are kept constant due to the gas molecules colliding more frequently with the walls of the container.