Which term refers to the process by which ions that have entered solution are kept in solution?
dissociation
electrolyte
hydration
ionization

Answer : The correct option is, hydration

Explanation :

Hydration : It is a process in which the ion or substance combines with water and kept in the solution. In the hydration process the solvent is water molecule.

For example : When the sodium chloride is dissolved in the water then the positive sodium ion get surrounded by the water molecule through their oxygen ends and the negative chloride ion get surrounded by the water molecule through their hydrogen ends.

Dissociation : It is a process in which the compound splits or dissociates into to two or more smaller ions, atoms or particles.

Electrolyte : it is a process in which the a molecule is completely dissociates into their respective ions in the aqueous solution.

Ionization : It is a process in which a molecule acquire a positive or negative charged by the gaining or losing electrons.

Hence, the correct option is, hydration.