What is isotonic solution?

If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrame. Such a solution is known as an isotonic solution. Water crosses the cell membrame in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. The cell will stay the same size.

If the medium in which the cell is kept is having same water concentration as the inside of the cell then there will be no net movement and the solution is called isotonic.