during passive transport what are the concentration of substances on either side of the membrane trying to reach

During passive transport, the concentration of substances on either side of the membrane are trying to reach equilibrium.

Explanation:

Passive transport can be described as the movement of molecules from a region of higher concentration to a region of lower concentration along a concentration gradient. As the molecule are higher at one side and lower on the other side, the molecules move so that there can be equal number of molecules on each side so that equilibrium can be reached and maintained.