Which type of solution would be used to hydrate dehydrated cells?

A hypotonic solution is the correct choice for hydrating dehydrated cells because it has a lower concentration of solutes compared to the inside of the cells. When cells are placed in a hypotonic environment, water naturally moves into the cells through osmosis. This influx of water occurs because the water molecules move from an area of higher concentration (outside of the cell) to an area of lower concentration (inside the cell), ultimately helping to restore hydration in the cells.

In contrast, a hypertonic solution contains a higher concentration of solutes compared to the cellular fluid, which would lead to water moving out of the cells, potentially causing them to become even more dehydrated. An isotonic solution has equal concentrations of solutes, meaning there is no net movement of water into or out of the cells, so while it maintains cell shape, it doesn’t actively hydrate dehydrated cells. A nil solution, or one with no solutes, wouldn't effectively deliver the needed osmotic gradient to facilitate hydration.