We can see here that Paramecium 3 have highest contraction rate.
Why is it so?
The water potential that would likely lead to the highest contraction rate in a paramecium would be a hypotonic solution.
Paramecia are single-celled organisms with contractile vacuoles that help regulate water intake and prevent the cell from bursting due to osmotic pressure. When placed in a hypotonic solution (a solution with lower solute concentration compared to the cell's cytoplasm), water moves into the paramecium by osmosis, causing the cell to swell.
The measure of water potential in a hypotonic solution can be described as having a higher water potential compared to the internal environment of a cell or organism.