Final answer:
The question involves helium gas escaping isothermally from a leaky cylinder, keeping the temperature constant (20 °C), and it relates to Chemistry in a High School educational level context.
Step-by-step explanation:
The question pertains to the behavior of gases in cylinders, particularly in the context of helium gas escaping from a cylinder through a leaky valve. When the gas escapes isothermally, it maintains a constant temperature (20 °C in this case). Due to the leaky valve situation presented, it's inferred that the gas expands to fill the space it escapes into, which would be at a lower pressure than the initial 120 atm inside the cylinder. Since the mass of helium is given (500 g), this information could be used to calculate the volume of gas released using the Ideal Gas Law as it expands to atmospheric pressure at constant temperature.