When a cell is placed in a hypertonic solution, it loses water. This occurs because the concentration of solutes outside the cell is higher than that inside the cell. As a result, water moves out of the cell in an attempt to balance the solute concentrations on both sides of the cell membrane.
This process is known as osmosis, which is the movement of water across a selectively permeable membrane. The loss of water causes the cell to shrink, a phenomenon often referred to as crenation in red blood cells.
In summary, in a hypertonic solution, a cell primarily loses water, leading to decreased cell volume and potential effects on cell function.