Final answer:
An isotonic enteral formula would have an osmolality of 300 mOsm/L, which is the same osmolarity as body fluids, thereby preventing net water movement across cell membranes.
Step-by-step explanation:
An isotonic enteral formula would have an osmolality similar to that of the body's fluids. The approximate osmolarity of body fluids is 300 mOsm/L, which is often considered isotonic and which means that there will be no net movement of water into or out of the cells when they are exposed to this solution. Therefore, the correct answer to the question is B. 300 mOsm/L. Saline solution and blood are examples of isotonic solutions with respect to body fluids.