Answer : The correct option is, D
Explanation :
Saturated solution : It is a chemical solution which contain the maximum amount of solute dissolved in the solvent. In saturated solution, the additional amount of solute will not dissolve in the solvent.
When a student has a solution of sodium nitrate then we can check their saturation point by adding additional amount of sodium nitrate. When we add more amount of sodium nitrate in the solution, then all of it will settle down to the bottom of the container.
Therefore, the best evidence for saturated solution is, When additional sodium nitrate is added, it all settles to the bottom of the container.