To determine which type of solution is at equilibrium, let's consider the definitions and characteristics of different types of solutions:
1. Concentrated Solution:
- A solution that has a relatively large amount of solute dissolved in a solvent.
2. Dilute Solution:
- A solution that has a relatively small amount of solute dissolved in a solvent.
3. Saturated Solution:
- A solution in which the maximum amount of solute has been dissolved at a given temperature and pressure. At this point, any additional solute added will not dissolve and will remain in its solid form.
4. Unsaturated Solution:
- A solution in which less than the maximum amount of solute has been dissolved. This means more solute can still dissolve in the solvent.
A solution that is at equilibrium regarding solubility must be saturated. Here’s why:
- In a saturated solution, there's a dynamic equilibrium between the dissolved solute molecules and the undissolved solute particles. At this state, the rate at which the solute dissolves is equal to the rate at which it precipitates out.
- Concentrated and dilute are relative terms describing the amount of solute, but they do not necessarily indicate an equilibrium state.
- An unsaturated solution is still capable of dissolving more solute, so it is not at equilibrium.
With these explanations, we can conclude that:
The solution that is at equilibrium must be saturated.
So, the correct answer is:
C) saturated
