What would most likely happen to an onion cell if it were placed in a liquid with a high concentration of solutes?

The liquid would be hypertonic towards the onion cell. This causes a net diffusion of water out from the onion cell into the surrounding liquid through osmosis. The onion cell is likely to wilt. If observed under a microscope, it is possible to view the plasma membrane pull away from the cell wall as well as a shrunken vacuole.