Final answer:
Absorption stops when all the unionized molecules are absorbed and only ions are left behind. This happens because the unionized molecules are the ones that are readily absorbed into a substance, such as a solvent.
Step-by-step explanation:
Absorption stops when all the unionized molecules are absorbed and only ions are left behind.
When a substance is absorbed, it can exist in different forms, including unionized molecules and ions. Unionized molecules are those that have not gained or lost any electrons and therefore do not carry a charge. On the other hand, ions are charged particles that have gained or lost electrons.
During absorption, the unionized molecules are typically the ones that are readily absorbed into a substance, such as a solvent. Once all the unionized molecules have been absorbed, only the ions, if any are present, remain behind. This is because ions may have a different chemical structure or charge, making them less likely to be absorbed.