Final answer:
The gas sample that will weigh the most is Nitrogen dioxide (NO2) because it has the highest molar mass of 46 g/mol among the options provided, and all gases occupy the same volume under the same conditions of temperature and pressure.
Step-by-step explanation:
To determine which gas sample will weigh the most, we need to consider the molar mass of each gas and the fact that, under the same conditions of temperature and pressure (in this case, 25 ℃ and 1 atmosphere), 1 mole of any gas will occupy the same volume due to Avogadro's law. A two-liter sample of each gas contains the same number of moles, so the gas with the highest molar mass will have the greatest weight.
The molar masses of the gases given are approximately:
Ammonia (NH3): 17 g/mol
Argon (Ar): 40 g/mol
Carbon dioxide (CO2): 44 g/mol
Nitrogen dioxide (NO2): 46 g/mol
Oxygen (O2): 32 g/mol
Given these molar masses, Nitrogen dioxide (NO2) with a molar mass of 46 g/mol will weigh the most for a two-liter sample at 25 ℃ and 1 atmosphere.