Final answer:
All four gases at 0 °C and 1 atm pressure have the same average kinetic energy because, according to the kinetic molecular theory, average kinetic energy is only dependent on temperature, not the type of gas.
Step-by-step explanation:
The question asks for the gas with the smallest average kinetic energy among four different gases, assuming all are ideal gases at the same conditions of temperature (0 °C) and pressure (1 atm). As per the kinetic molecular theory, the average kinetic energy (average kinetic energy) of a gas is directly proportional to the absolute temperature of the gas and does not depend on the identity of the gas molecules.
Therefore, since all gases are at the same temperature, they all have the same average kinetic energy per molecule. The types of molecules present in the gas do not affect the average kinetic energy; it's only temperature-dependent.
The average kinetic energy of gas molecules is directly related to their temperature. So, for which gas do the molecules have the smallest average kinetic energy? The gas with the lowest temperature. In this case, since all gases are at 0 °C, we need to look at the molecular masses to determine the gas with the smallest average kinetic energy.
Helium (He) has the smallest molecular mass, so the molecules of helium in the flasks will have the smallest average kinetic energy. Therefore, the answer is B) Helium.