Answer: Facilitated Diffusion.
Explanation:
Most substances use simple diffusion, move across a membrane because they are smaller and polar. But for chloride ions, that is not the case.
Chloride Ions are charged negatively, and since they are negatively charged, they cannon move across the membrane without help from something. Therefore, chloride ions move by facilitated diffusion using carrier proteins.
Facilitated Diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins.
That explains how chloride ions can move in and out of cells.
