Final answer:
Measurements that must be made to calculate the molar mass of a gas include mass, pressure, volume, and temperature, but not the water levels inside and outside the gas collection tube.
Step-by-step explanation:
Measurements that must be made to calculate the molar mass of the gas include the mass, pressure, volume, and temperature of the gas sample. However, the water levels inside and outside the gas collection tube being made the same is not a measurement that directly contributes to the calculation of the molar mass. It is simply a step to ensure that the gas sample has been completely collected.