In a system with a semipermeable membrane, why does the side with higher mobility ions become more positively charged?

• A. Because ions with higher mobility do not move at all.
• B. Because ions with higher mobility move faster, leaving behind slower-moving ions, creating a charge imbalance.
• C. Because ions with higher mobility are negatively charged and accumulate on one side.
• D. Because ions with higher mobility are repelled by the membrane.

Answer: (B)