Final answer:
The osmolarity of body fluids is maintained at approximately 300 mOsm/L, which is isotonic with the body's cells to prevent osmotic imbalances.
Step-by-step explanation:
The osmolarity of body fluids is crucial for maintaining cellular function and overall homeostasis. The body has several mechanisms that regulate both water intake and water output to keep body fluid concentrations within a narrow range. The correct answer to the osmolarity of body fluids is 300 mOsm/L. This concentration level is isotonic with the body's cellular environment, preventing cell shrinkage or swelling due to osmosis. The body's osmoregulation abilities ensure that the osmolarity stays consistent and is tightly monitored to stay in the range of approximately 280 to 300 mOsm/L.