State the technical term for a medium which has exactly the same concentration as the cell?Why does the size of the cell remain the same when placed in such a solution?

Isotonic solution is the medium which has exactly the same concentration as the cell. This results in osmotic balance as their no net movement of water or solutes into or outside the cell i.e movement of water or solute inside the cell is equal to their movement outside the cell. Hence, the size of the cell remain the same when placed in such a solution.