When an equilibrium exists between the dissolved and the undissolved solute in a solution the solution must be?

When an equilibrium exists between the dissolved and the undissolved solute in a solution; the solution must be Saturated. 
With respect to solutions, a saturated solution is a solution that has the same concentration it would have if it were in equilibrium with undissolved solute, In other words it defines an equilibrium property, and a temperature is normally specified because a hot solution can dissolve more solute than a cold one.

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