Which IV solution is isotonic?

Rationale: A. 0.45% sodium chloride is incorrect because this is a hypotonic solution, meaning it has a lower solute concentration than blood. It draws water into cells, which can cause cellular swelling, and is used to treat cellular dehydration, not for maintaining fluid balance like isotonic solutions. B. 0.9% sodium chloride is correct because it is isotonic, having a solute concentration similar to that of blood plasma. Isotonic solutions maintain fluid balance in the intravascular space without causing fluid shifts into or out of cells, making it ideal for fluid resuscitation, IV access maintenance, and initial treatment of dehydration. C. 3% sodium chloride is incorrect because this is a hypertonic solution, with a higher solute concentration than blood. It pulls water out of cells into the intravascular space, and is used cautiously in conditions like hyponatremia. Rapid administration can cause cellular dehydration and circulatory overload. D. D10W (10% dextrose in water) is incorrect because it is hypertonic in the bag but becomes hypotonic after dextrose is metabolized. It is used primarily for providing calories and fluid, not as an isotonic solution for maintaining fluid balance.