The answer is D: Saturated.
A saturated solution is one in which the exact maximum amount of solute has been dissolved. So, new solute will not dissolve in the solution. In contrast, an unsaturated solution can hold more solute, so if that option were correct, the crystal would have dissolved.
The other two terms are a bit more complicated. A supersaturated solution is one holding an amount of solute above the sustainable limit. Because of that, when more solute is added, the solution will immediately adjust, and some solute will come out of solution in a precipitate. Because the crystal isn't growing, we can eliminate this option.
A concentrated solution is one holding a relatively large amount of solute. However, you can have concentrated solutions that are saturated and unconcentrated (the word for this is dilute) solutions that aren't saturated. Therefore, we can say that because the crystal doesn't dissolve, this solution is saturated, but we can't say with certainty that it is concentrated.
Because the first three options are invalid, as described above, while the scenario does describe a saturated solution, D is the correct answer.
