Final answer:
The flask with the greatest average speed of molecules would be the one at a higher temperature, as this increases both the average kinetic energy and the root mean square speed.
Step-by-step explanation:
The molecules in a flask with the greatest average speed would be those at higher temperatures according to the Maxwell-Boltzmann distribution of molecular speeds. Since the average kinetic energy of molecules is proportional to the absolute temperature, as temperature increases, so does the average molecular speed. Additionally, root mean square speed (Vrms) is related to the average kinetic energy, which doubles when the average kinetic energy doubles, leading to an increase in Vrms to √2 times its initial value.
In context with the provided reference, flask (b) should have the molecules with the greatest average speed, as this is where the conditions are such that molecules have high speeds, suggesting higher temperature and energy levels.