The correct response is:
the number of moles of each gas
At the same pressure, volume, and temperature, the ideal gas law (PV = nRT) shows that the number of moles (n) can vary between different gases, as each gas can have a different molar mass. Therefore, the number of moles can differ even though the pressure, volume, and temperature are the same.
The other options are not correct because:
- The molar volume of each gas at the same conditions of temperature and pressure will be the same (ideal gas behavior).
- The gas constant (R) is a universal constant when using the ideal gas law, irrespective of the type of gas.
- The mass of each gas will depend on the number of moles and the molar mass, so it can also differ, but this is inherently tied to the number of moles and the molar mass.
Therefore, the number of moles is the most direct and simplest answer.