In the scenario you provided, since the gases are held at the same pressure, volume, and temperature, the quantity that can differ between the two gases is the number of moles of each gas.
According to the ideal gas law (PV = nRT), at the same pressure (P), volume (V), and temperature (T), different gases can have different amounts (moles, n) because they can have different molar masses. Therefore, the number of moles can differ while other quantities remain the same.
To summarize:
- The gas constant is specific to each gas and is not a variable.
- The molar volume under the same conditions for an ideal gas is the same for all, but not for real gases.
- The mass of each gas can vary based on the number of moles and molar mass, but it is not the primary answer to the scenario given.
So, the correct answer is the number of moles of each gas.