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------------------------------------------------ How many meq of sodium are contained in 250 ml of a solution of sodium bicarbonate that is isoosmotic with plasma that is 300 mosm/l?

A. 50 meq
B. 75 meq
C. 100 meq
D. 125 meq

To calculate the number of milliequivalents (meq) of sodium in an isoosmotic solution, we must first understand what isoosmotic means. An isoosmotic solution has the same osmolality as plasma, which, as noted in the question, is approximately 300 milliosmoles per liter (mOsm/L). Sodium bicarbonate (NaHCO3), when dissolved in water, dissociates into one sodium ion (Na+) and one bicarbonate ion (HCO3-), each contributing to the osmolality of the solution.

Since isoosmotic solutions have the same osmolality as plasma, a 300 mOsm/L solution of sodium bicarbonate would contain 300 milliosmoles of Na+ per liter. Remember, one meq of Na+ is equal to one millimole by definition as the valency of sodium is 1. Therefore, 300 milliosmoles is equivalent to 300 milliequivalents (meq) of sodium per liter.
To find the amount in 250 mL, we perform the following calculation:

(300 meq/L) * (0.250 L) = 75 meq

Therefore, the correct answer is b. 75 meq of sodium in 250 mL of an isoosmotic sodium bicarbonate solution.