Why will the molecules move from right to left through the cell membrane?

The molecules move from right to left through the cell membrane due to diffusion.

Explanation:

Diffusion is a process in which molecule move from the region of higher concentration to the region of lower concentration. If substances such as salts, water etc are present in high quantity inside the cell, so it moves outside the cell through cell membrane or if the concentration of molecules are higher outside the cell so it moves inside the cell. This inside and outside movement of molecules is called diffusion.