What would most likely happened to a unicelluar organism if it was exposed to a hypotonic solution for an extended period of time

It would swell and then bust.

Explanation:

In a hypotonic solution, the water concentration of the cell's cytoplasm is lower than the concentration of the hypotonic solution. If a unicellular organism is exposed to a hypotonic solution, the water from the solution will enter gradually into the organism by the osmosis process. The aim is to keep a balance between water concentration on the inside and outside of the organism. But, that water that enters into the cytoplasm of the cell makes pressure on the cell membrane.

If the excess water cannot be removed from the organism, it will swell first and then, will burst.