What do you understand by Osmosis? …

It is the process of movement of water from its high concentration region to its low concentration region through semi-permeable membrane.
(i) Hypotonic Solution:
If the medium surrounding the cell has a higher water concentration than the cell, i.e., if the solution is very dilute solution, then the cell will gain water by osmosis. Such dilute solution is called Hypotonic solution.

(ii) Isotonic Solution:

If the medium surrounding the cell is of exactly the same water concentration as inside the cell, there will be no net movement of water across membrane resulting in no change in size of cell. Such solution is called Isotonic solution.

(iii) Hypertonic solution:

If the medium surrounding the cell has a lower water concentration than inside the cell, i.e., if the solution is highly concentrated, then the cell will lose water through osmosis. Such concentrated solution is called Hypertonic solution.