The correct response is:
the number of moles of each gas
Explanation: For gases at the same pressure, volume, and temperature, according to the ideal gas law (PV = nRT), the number of moles (n) will depend on the specific gas's molar mass. Therefore, even if the pressure, volume, and temperature are the same, the number of moles (and thus the mass) can differ between the two gases. The gas constant (R) is a universal value and does not differ between gases, and the molar volume is defined in terms of moles.