In the above question, if the bag refers to a dialysis bag, the membrane of a dialysis bag is a selectively permeable membrane that does not allow the movement of all molecules to diffuse across the ,membrane. Osmosis is best explained with the help of a dialysis bag. In the process of osmosis the movement of water molecules from their higher concentration to lower concentration take place across the membrane.
Thus, only water molecules will pass across the bag and limit the movement of other molecules.
