When a red blood cell is placed in a hypertonic solution, which will occur?

If a red blood cell is placed in a hypertonic solution, the cell would shrink.

Hypertonic solution means that the solution has a lower water potential than the other side (which is the cell's cytoplasm in this case), and by that, water molecules would have a tendency to flow from a region of higher water potential to a region of lower water potential. This movement of water molecules is called osmosis. But note that a semi-permeable membrane (a membrane which can decide what substances can go in and out, the cell membrane is an example) has to be present in osmosis, or else the movement may be regarded as diffusion.

As the water molecules flowed away from the red blood cell cytoplasm, the cell loss so much water that the membrane has nothing much to hold and thus the cell shrinks.