Diffusion is a type of passive transport that implies the movement of molecules from a place with a higher concentration of the solute to a place with a lower concentration of the solute, without waste of energy. This movement occurs until it is reached a dynamic equilibrium, which means that the same amount of molecules of the solute moves from both places (in and out). When this equilibrium is reached the mass stays steady.
Therefore, for this case in particular, the bag that will show the least change in mass will be the one that is in a dynamic equilibrium with its external environment, not showing any mass change at all. This condition is given in sample 3.