The CO₂ balloon contains the greatest mass of gas because CO₂ has the highest molar mass (44 g/mol) among the gases listed.
The average kinetic energy of gas molecules depends on temperature, not on the type of gas. At the same temperature, all gases have the same average kinetic energy.
According to the kinetic theory of gases, the average kinetic energy of gas molecules is given by (3/2)kT, where k is the Boltzmann constant and T is the temperature.
The average kinetic energies of the gas molecules in all the balloons are the same because they are all at the same temperature (0°C).