Final answer:
After concentration equalizes, particles continue their random movement with no net change in concentration over time, which is termed dynamic equilibrium. They cross the membrane at equal rates in both directions, maintaining equilibrium. Therefore correct option is A
Step-by-step explanation:
Once the concentration has equalized throughout the solution, particles continue their random movement as before, but an equal number move from right to left as they do from left to right. This conclusion is based on the principles of diffusion and dynamic equilibrium. As diffusion progresses, molecules move from an area of high concentration to an area of lower concentration until equilibrium is reached. At this point, there is no longer a net movement of molecules across the membrane because for every molecule that crosses in one direction, another crosses in the opposite direction. This movement is not due to molecules simply jiggling on their own side of the membrane; they can and do cross the membrane, maintaining an equilibrium of concentration.
Molecules in a gas, liquid, or solid are always in motion due to their kinetic energy. Their collisions cause a random direction of movement, leading to diffusion through available space until an even distribution is achieved. Even after a substance has diffused completely, resulting in no concentration gradient, molecules continue to move within the space. Thus, the lack of net movement in number of molecules defines the state of dynamic equilibrium in diffusion processes.