Which organelle forms the surface of a cell separating its content from the outside world?

Cell membrane is the organelle forms the surface of a cell separating its content from the outside world.

Explanation:It is outer most layer of cell which is a barrier for molecules and ions freely floating outside to enter the cell.It is usually made up of lipid bilayer with some proteins embedded in it.The lipid layer made it hydrophobic which repels water content from both sides.Water content (cytoplasm ) of cell remains in cell due to cell membrane.

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Ithink that b is correct but just in case wait to see if someone else answers