Question

Diffusion continues until the concentration on both sides of the membrane is

Answer 1

I don't completely understand the question, but I am guessing that you are trying to finish the sentence. If so, the answer is "Diffusion continues until the concentration on both sides of the membrane is equal". The reason it's equal is because diffusion always travels high to low, to reach a point of equilibrium. The particles are trying to move so that water is the same inside and outside of the cell/membrane, and the solute is also equal on the inside and outside of the cell/membrane. If that doesn't make sense, just comment any questions you have and I will try my best to answer :)

Answer 2

Diffusion is the process in which movement of molecules , ions, and atoms take place from region of higher concnetration to low concentration.  This  diffusion will continues till both side of membrane is equal, because it is the movement of molecule from high to low concentration, so once its became equal concnetration diffusion will not take place.