Question

A plant cell is kept in a hypotonic solution, what will happen to the solute potential of the cell?

Answer 1

The fluid in the plant cell is at a higher concentration than the hypotonic (solution) fluid outside the cell membrane.   So the fluid (solvent) flows in (osmosis process) through the membrane of the cell.   The cell size increases, the cell swells or expands.

So the solute potential inside the cell decreases.