An isotonic solution for human red blood cells is a solution with the same concentration of solutes as the inside of the red blood cells. This means that the water potential inside and outside the cell is equal, so there is no net movement of water across the cell membrane.

Here are some examples of solutions that are considered isotonic to human red blood cells:

* 0.9% NaCl solution (also known as normal saline)

* 5% dextrose solution (also known as D5W)

It's important to note that "isotonic" is a relative term. A solution that is isotonic to red blood cells might not be isotonic to other types of cells.