Final answer:
The initial fluid used to treat dehydration is isotonic, which has the same osmolarity as the body's cells.
Step-by-step explanation:
The type of fluid that is initially used to treat dehydration is isotonic.
An isotonic solution has the same osmolarity as the body's cells, which means it has a similar concentration of solutes as the cells. This helps to replenish the body's fluid volume without causing an imbalance in the osmolarity of the cells.
Examples of isotonic solutions that can be used to treat dehydration include 0.9% m/v NaCl solution in water and 5% m/v glucose solution in water.