Is a. wrong because mixture of solute and solvent is not a reaction?
Answer credited to @Asafmen
The correct answer is C.
If a solution of salt and water is saturated, water will not turn into salt and salt will not turn into water. It simply means that there is an abundance of salt in the after, and so little water comparitevly- that any additional salt will not dissolve.
When a solution is saturated, we have the most solute possible dissolved within the solvent, meaning the concentration of the solute in the solution is at its maximum.
Logically, the relative water amount in the solution will be minimal and relative to the solute- the amount of solvent is minimal.